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 $208.91   5.650%   $220.7134   $220.71   $220.70   $220.70  
  Purchase #2 $48.79   4.465%   $50.9685   $50.97   $50.95   $51.00  
  Purchase #3 $215.53   6.259%   $229.02   $229.02   $229.00   $229.00  
  Purchase #4 $96.89   6.251%   $102.9466   $102.95   $102.95   $102.90  
  Purchase #5 $139.70   7.830%   $150.6385   $150.64   $150.65   $150.60  
  Purchase #6 $217.39   11.774%   $242.9855   $242.99   $243.00   $243.00  
  Purchase #7 $242.93   3.319%   $250.9928   $250.99   $251.00   $251.00  
  7 purchase totals = $1,170.14       $1,248.2653   $1,248.27   $1,248.25   $1,248.20