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 $46.32   13.352%   $52.5046   $52.50   $52.50   $52.50  
  Purchase #2 $175.34   10.370%   $193.5228   $193.52   $193.50   $193.50  
  Purchase #3 $122.74   8.659%   $133.3681   $133.37   $133.35   $133.40  
  Purchase #4 $67.78   9.156%   $73.9859   $73.99   $74.00   $74.00  
  Purchase #5 $129.64   3.398%   $134.0452   $134.05   $134.05   $134.00  
  Purchase #6 $237.75   7.412%   $255.372   $255.37   $255.35   $255.40  
  Purchase #7 $230.74   9.545%   $252.7641   $252.76   $252.75   $252.80  
  7 purchase totals = $1,010.31       $1,095.5627   $1,095.56   $1,095.50   $1,095.60