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 $51.72   13.724%   $58.8181   $58.82   $58.80   $58.80  
  Purchase #2 $192.52   10.475%   $212.6865   $212.69   $212.70   $212.70  
  Purchase #3 $230.88   11.645%   $257.766   $257.77   $257.75   $257.80  
  Purchase #4 $21.80   11.538%   $24.3153   $24.32   $24.30   $24.30  
  Purchase #5 $114.87   6.148%   $121.9322   $121.93   $121.95   $121.90  
  Purchase #6 $182.94   9.514%   $200.3449   $200.34   $200.35   $200.30  
  Purchase #7 $149.46   5.341%   $157.4427   $157.44   $157.45   $157.40  
  7 purchase totals = $944.19       $1,033.3057   $1,033.31   $1,033.30   $1,033.20