Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $185.96   9.663%   $203.9293   $203.93   $203.95   $203.90  
  Purchase #2 $136.96   12.228%   $153.7075   $153.71   $153.70   $153.70  
  Purchase #3 $110.95   12.669%   $125.0063   $125.01   $125.00   $125.00  
  Purchase #4 $166.48   13.486%   $188.9315   $188.93   $188.95   $188.90  
  Purchase #5 $144.75   4.461%   $151.2073   $151.21   $151.20   $151.20  
  Purchase #6 $162.27   9.481%   $177.6548   $177.65   $177.65   $177.70  
  Purchase #7 $199.66   13.224%   $226.063   $226.06   $226.05   $226.10  
  7 purchase totals = $1,107.03       $1,226.4997   $1,226.50   $1,226.50   $1,226.50