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 $60.88   6.717%   $64.9693   $64.97   $64.95   $65.00  
  Purchase #2 $63.40   12.132%   $71.0917   $71.09   $71.10   $71.10  
  Purchase #3 $75.84   12.691%   $85.4649   $85.46   $85.45   $85.50  
  Purchase #4 $127.58   9.746%   $140.0139   $140.01   $140.00   $140.00  
  Purchase #5 $57.29   5.387%   $60.3762   $60.38   $60.40   $60.40  
  Purchase #6 $233.97   13.826%   $266.3187   $266.32   $266.30   $266.30  
  Purchase #7 $53.80   7.708%   $57.9469   $57.95   $57.95   $57.90  
  7 purchase totals = $672.76       $746.1816   $746.18   $746.15   $746.20