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 $174.74   12.798%   $197.1032   $197.10   $197.10   $197.10  
  Purchase #2 $201.79   9.484%   $220.9278   $220.93   $220.95   $220.90  
  Purchase #3 $149.35   4.423%   $155.9558   $155.96   $155.95   $156.00  
  Purchase #4 $50.72   10.228%   $55.9076   $55.91   $55.90   $55.90  
  Purchase #5 $45.80   4.714%   $47.959   $47.96   $47.95   $48.00  
  Purchase #6 $124.47   10.359%   $137.3638   $137.36   $137.35   $137.40  
  Purchase #7 $244.57   5.292%   $257.5126   $257.51   $257.50   $257.50  
  7 purchase totals = $991.44       $1,072.7298   $1,072.73   $1,072.70   $1,072.80