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 $184.71   4.478%   $192.9813   $192.98   $193.00   $193.00  
  Purchase #2 $210.95   7.117%   $225.9633   $225.96   $225.95   $226.00  
  Purchase #3 $134.82   6.119%   $143.0696   $143.07   $143.05   $143.10  
  Purchase #4 $150.40   6.109%   $159.5879   $159.59   $159.60   $159.60  
  Purchase #5 $87.31   12.807%   $98.4918   $98.49   $98.50   $98.50  
  Purchase #6 $86.70   11.481%   $96.654   $96.65   $96.65   $96.70  
  Purchase #7 $237.64   5.165%   $249.9141   $249.91   $249.90   $249.90  
  7 purchase totals = $1,092.53       $1,166.6620   $1,166.65   $1,166.65   $1,166.80