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 $138.75   9.590%   $152.0561   $152.06   $152.05   $152.10  
  Purchase #2 $193.72   3.585%   $200.6649   $200.66   $200.65   $200.70  
  Purchase #3 $152.53   12.410%   $171.459   $171.46   $171.45   $171.50  
  Purchase #4 $62.87   8.396%   $68.1486   $68.15   $68.15   $68.10  
  Purchase #5 $183.95   11.596%   $205.2808   $205.28   $205.30   $205.30  
  Purchase #6 $55.63   7.754%   $59.9436   $59.94   $59.95   $59.90  
  Purchase #7 $116.26   8.475%   $126.113   $126.11   $126.10   $126.10  
  7 purchase totals = $903.71       $983.6660   $983.66   $983.65   $983.70