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 $52.49   11.710%   $58.6366   $58.64   $58.65   $58.60  
  Purchase #2 $206.69   5.438%   $217.9298   $217.93   $217.95   $217.90  
  Purchase #3 $52.31   13.538%   $59.3917   $59.39   $59.40   $59.40  
  Purchase #4 $91.50   12.391%   $102.8378   $102.84   $102.85   $102.80  
  Purchase #5 $42.32   11.271%   $47.0899   $47.09   $47.10   $47.10  
  Purchase #6 $202.77   11.207%   $225.4944   $225.49   $225.50   $225.50  
  Purchase #7 $54.63   11.434%   $60.8764   $60.88   $60.90   $60.90  
  7 purchase totals = $702.71       $772.2566   $772.26   $772.35   $772.20