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 $53.37   9.468%   $58.4231   $58.42   $58.40   $58.40  
  Purchase #2 $169.79   9.448%   $185.8318   $185.83   $185.85   $185.80  
  Purchase #3 $217.35   4.287%   $226.6678   $226.67   $226.65   $226.70  
  Purchase #4 $207.72   7.797%   $223.9159   $223.92   $223.90   $223.90  
  Purchase #5 $126.78   9.727%   $139.1119   $139.11   $139.10   $139.10  
  Purchase #6 $63.53   12.489%   $71.4643   $71.46   $71.45   $71.50  
  Purchase #7 $209.63   4.756%   $219.6   $219.60   $219.60   $219.60  
  7 purchase totals = $1,048.17       $1,125.0148   $1,125.01   $1,124.95   $1,125.00