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 $162.71   12.581%   $183.1805   $183.18   $183.20   $183.20  
  Purchase #2 $203.73   10.791%   $225.7145   $225.71   $225.70   $225.70  
  Purchase #3 $232.65   5.758%   $246.046   $246.05   $246.05   $246.00  
  Purchase #4 $239.27   10.627%   $264.6972   $264.70   $264.70   $264.70  
  Purchase #5 $159.25   8.149%   $172.2273   $172.23   $172.25   $172.20  
  Purchase #6 $218.79   4.657%   $228.9791   $228.98   $229.00   $229.00  
  Purchase #7 $39.42   9.200%   $43.0466   $43.05   $43.05   $43.00  
  7 purchase totals = $1,255.82       $1,363.8912   $1,363.90   $1,363.95   $1,363.80