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 $55.70   11.663%   $62.1963   $62.20   $62.20   $62.20  
  Purchase #2 $229.69   5.194%   $241.6201   $241.62   $241.60   $241.60  
  Purchase #3 $216.70   7.445%   $232.8333   $232.83   $232.85   $232.80  
  Purchase #4 $39.53   8.612%   $42.9343   $42.93   $42.95   $42.90  
  Purchase #5 $23.83   3.344%   $24.6269   $24.63   $24.65   $24.60  
  Purchase #6 $234.43   4.276%   $244.4542   $244.45   $244.45   $244.50  
  Purchase #7 $183.32   3.405%   $189.562   $189.56   $189.55   $189.60  
  7 purchase totals = $983.20       $1,038.2271   $1,038.22   $1,038.25   $1,038.20