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 $92.38   10.716%   $102.2794   $102.28   $102.30   $102.30  
  Purchase #2 $89.95   7.429%   $96.6324   $96.63   $96.65   $96.60  
  Purchase #3 $157.82   4.842%   $165.4616   $165.46   $165.45   $165.50  
  Purchase #4 $70.46   7.502%   $75.7459   $75.75   $75.75   $75.70  
  Purchase #5 $167.74   8.172%   $181.4477   $181.45   $181.45   $181.40  
  Purchase #6 $50.77   9.464%   $55.5749   $55.57   $55.55   $55.60  
  Purchase #7 $107.79   12.870%   $121.6626   $121.66   $121.65   $121.70  
  7 purchase totals = $736.91       $798.8045   $798.80   $798.80   $798.80