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 $86.85   8.196%   $93.9682   $93.97   $93.95   $94.00  
  Purchase #2 $149.34   8.550%   $162.1086   $162.11   $162.10   $162.10  
  Purchase #3 $141.55   5.624%   $149.5108   $149.51   $149.50   $149.50  
  Purchase #4 $161.64   7.704%   $174.0927   $174.09   $174.10   $174.10  
  Purchase #5 $137.94   8.672%   $149.9022   $149.90   $149.90   $149.90  
  Purchase #6 $185.92   4.722%   $194.6991   $194.70   $194.70   $194.70  
  Purchase #7 $59.76   9.325%   $65.3326   $65.33   $65.35   $65.30  
  7 purchase totals = $923.00       $989.6142   $989.61   $989.60   $989.60