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 $81.67   13.559%   $92.7436   $92.74   $92.75   $92.70  
  Purchase #2 $244.85   9.399%   $267.8635   $267.86   $267.85   $267.90  
  Purchase #3 $70.94   9.452%   $77.6452   $77.65   $77.65   $77.60  
  Purchase #4 $144.52   6.721%   $154.2332   $154.23   $154.25   $154.20  
  Purchase #5 $138.47   9.567%   $151.7174   $151.72   $151.70   $151.70  
  Purchase #6 $68.27   13.677%   $77.6073   $77.61   $77.60   $77.60  
  Purchase #7 $140.30   10.695%   $155.3051   $155.31   $155.30   $155.30  
  7 purchase totals = $889.02       $977.1153   $977.12   $977.10   $977.00