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 $139.56   8.262%   $151.0904   $151.09   $151.10   $151.10  
  Purchase #2 $216.53   7.313%   $232.3648   $232.36   $232.35   $232.40  
  Purchase #3 $131.46   13.690%   $149.4569   $149.46   $149.45   $149.50  
  Purchase #4 $240.31   10.679%   $265.9727   $265.97   $265.95   $266.00  
  Purchase #5 $120.48   4.462%   $125.8558   $125.86   $125.85   $125.90  
  Purchase #6 $190.61   10.674%   $210.9557   $210.96   $210.95   $211.00  
  Purchase #7 $227.41   3.579%   $235.549   $235.55   $235.55   $235.50  
  7 purchase totals = $1,266.36       $1,371.2453   $1,371.25   $1,371.20   $1,371.40