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 $66.51   3.746%   $69.0015   $69.00   $69.00   $69.00  
  Purchase #2 $169.95   13.799%   $193.4014   $193.40   $193.40   $193.40  
  Purchase #3 $120.95   12.178%   $135.6793   $135.68   $135.70   $135.70  
  Purchase #4 $17.90   6.136%   $18.9983   $19.00   $19.00   $19.00  
  Purchase #5 $179.78   3.220%   $185.5689   $185.57   $185.55   $185.60  
  Purchase #6 $205.71   3.374%   $212.6507   $212.65   $212.65   $212.70  
  Purchase #7 $83.66   13.865%   $95.2595   $95.26   $95.25   $95.30  
  7 purchase totals = $844.46       $910.5596   $910.56   $910.55   $910.70