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 $63.96   3.149%   $65.9741   $65.97   $65.95   $66.00  
  Purchase #2 $150.89   12.313%   $169.4691   $169.47   $169.45   $169.50  
  Purchase #3 $119.55   12.134%   $134.0562   $134.06   $134.05   $134.10  
  Purchase #4 $88.73   5.130%   $93.2818   $93.28   $93.30   $93.30  
  Purchase #5 $148.68   5.594%   $156.9972   $157.00   $157.00   $157.00  
  Purchase #6 $239.68   10.527%   $264.9111   $264.91   $264.90   $264.90  
  Purchase #7 $39.39   5.569%   $41.5836   $41.58   $41.60   $41.60  
  7 purchase totals = $850.88       $926.2731   $926.27   $926.25   $926.40