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 $57.54   8.713%   $62.5535   $62.55   $62.55   $62.60  
  Purchase #2 $131.33   6.194%   $139.4646   $139.46   $139.45   $139.50  
  Purchase #3 $213.99   7.782%   $230.6427   $230.64   $230.65   $230.60  
  Purchase #4 $23.83   6.678%   $25.4214   $25.42   $25.40   $25.40  
  Purchase #5 $214.40   6.279%   $227.8622   $227.86   $227.85   $227.90  
  Purchase #6 $185.42   5.447%   $195.5198   $195.52   $195.50   $195.50  
  Purchase #7 $230.65   13.121%   $260.9136   $260.91   $260.90   $260.90  
  7 purchase totals = $1,057.16       $1,142.3778   $1,142.36   $1,142.30   $1,142.40