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 $68.27   6.681%   $72.8311   $72.83   $72.85   $72.80  
  Purchase #2 $168.59   5.362%   $177.6298   $177.63   $177.65   $177.60  
  Purchase #3 $137.43   4.567%   $143.7064   $143.71   $143.70   $143.70  
  Purchase #4 $148.90   11.547%   $166.0935   $166.09   $166.10   $166.10  
  Purchase #5 $126.50   9.821%   $138.9236   $138.92   $138.90   $138.90  
  Purchase #6 $68.37   9.532%   $74.887   $74.89   $74.90   $74.90  
  Purchase #7 $127.92   6.525%   $136.2668   $136.27   $136.25   $136.30  
  7 purchase totals = $845.98       $910.3382   $910.34   $910.35   $910.30