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 $187.37   7.591%   $201.5933   $201.59   $201.60   $201.60  
  Purchase #2 $222.74   4.526%   $232.8212   $232.82   $232.80   $232.80  
  Purchase #3 $244.27   3.214%   $252.1208   $252.12   $252.10   $252.10  
  Purchase #4 $85.82   11.463%   $95.6575   $95.66   $95.65   $95.70  
  Purchase #5 $48.86   10.401%   $53.9419   $53.94   $53.95   $53.90  
  Purchase #6 $224.79   8.373%   $243.6117   $243.61   $243.60   $243.60  
  Purchase #7 $157.36   8.466%   $170.6821   $170.68   $170.70   $170.70  
  7 purchase totals = $1,171.21       $1,250.4285   $1,250.42   $1,250.40   $1,250.40