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 $56.85   12.477%   $63.9432   $63.94   $63.95   $63.90  
  Purchase #2 $153.52   13.341%   $174.0011   $174.00   $174.00   $174.00  
  Purchase #3 $81.97   3.424%   $84.7767   $84.78   $84.80   $84.80  
  Purchase #4 $57.38   10.186%   $63.2247   $63.22   $63.20   $63.20  
  Purchase #5 $58.71   11.306%   $65.3478   $65.35   $65.35   $65.30  
  Purchase #6 $212.30   13.686%   $241.3554   $241.36   $241.35   $241.40  
  Purchase #7 $116.51   6.518%   $124.1041   $124.10   $124.10   $124.10  
  7 purchase totals = $737.24       $816.7530   $816.75   $816.75   $816.70