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 $215.90   8.212%   $233.6297   $233.63   $233.65   $233.60  
  Purchase #2 $97.82   10.132%   $107.7311   $107.73   $107.75   $107.70  
  Purchase #3 $182.49   13.205%   $206.5878   $206.59   $206.60   $206.60  
  Purchase #4 $71.55   5.707%   $75.6334   $75.63   $75.65   $75.60  
  Purchase #5 $153.50   11.182%   $170.6644   $170.66   $170.65   $170.70  
  Purchase #6 $134.76   11.668%   $150.4838   $150.48   $150.50   $150.50  
  Purchase #7 $54.65   13.645%   $62.107   $62.11   $62.10   $62.10  
  7 purchase totals = $910.67       $1,006.8372   $1,006.83   $1,006.90   $1,006.80