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 $55.53   6.188%   $58.9662   $58.97   $58.95   $59.00  
  Purchase #2 $87.79   11.130%   $97.561   $97.56   $97.55   $97.60  
  Purchase #3 $231.78   5.804%   $245.2325   $245.23   $245.25   $245.20  
  Purchase #4 $219.32   4.265%   $228.674   $228.67   $228.65   $228.70  
  Purchase #5 $208.40   9.485%   $228.1667   $228.17   $228.15   $228.20  
  Purchase #6 $207.73   13.132%   $235.0091   $235.01   $235.00   $235.00  
  Purchase #7 $89.47   9.379%   $97.8614   $97.86   $97.85   $97.90  
  7 purchase totals = $1,100.02       $1,191.4709   $1,191.47   $1,191.40   $1,191.60