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 $55.92   8.353%   $60.591   $60.59   $60.60   $60.60  
  Purchase #2 $202.76   9.404%   $221.8276   $221.83   $221.85   $221.80  
  Purchase #3 $148.80   12.149%   $166.8777   $166.88   $166.90   $166.90  
  Purchase #4 $189.85   4.624%   $198.6287   $198.63   $198.65   $198.60  
  Purchase #5 $49.48   8.121%   $53.4983   $53.50   $53.50   $53.50  
  Purchase #6 $187.38   7.637%   $201.6902   $201.69   $201.70   $201.70  
  Purchase #7 $39.42   5.858%   $41.7292   $41.73   $41.75   $41.70  
  7 purchase totals = $873.61       $944.8427   $944.85   $944.95   $944.80