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 $201.91   7.474%   $217.0008   $217.00   $217.00   $217.00  
  Purchase #2 $151.47   11.647%   $169.1117   $169.11   $169.10   $169.10  
  Purchase #3 $95.92   11.161%   $106.6256   $106.63   $106.65   $106.60  
  Purchase #4 $133.64   8.430%   $144.9059   $144.91   $144.90   $144.90  
  Purchase #5 $140.47   7.217%   $150.6077   $150.61   $150.60   $150.60  
  Purchase #6 $65.77   5.431%   $69.342   $69.34   $69.35   $69.30  
  Purchase #7 $88.32   8.460%   $95.7919   $95.79   $95.80   $95.80  
  7 purchase totals = $877.50       $953.3856   $953.39   $953.40   $953.30