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 $29.83   8.414%   $32.3399   $32.34   $32.35   $32.30  
  Purchase #2 $153.50   10.174%   $169.1171   $169.12   $169.10   $169.10  
  Purchase #3 $245.78   10.724%   $272.1374   $272.14   $272.15   $272.10  
  Purchase #4 $219.93   12.317%   $247.0188   $247.02   $247.00   $247.00  
  Purchase #5 $67.93   11.390%   $75.6672   $75.67   $75.65   $75.70  
  Purchase #6 $227.46   13.823%   $258.9018   $258.90   $258.90   $258.90  
  Purchase #7 $246.83   7.316%   $264.8881   $264.89   $264.90   $264.90  
  7 purchase totals = $1,191.26       $1,320.0703   $1,320.08   $1,320.05   $1,320.00