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 $215.48   13.110%   $243.7294   $243.73   $243.75   $243.70  
  Purchase #2 $67.73   8.573%   $73.5365   $73.54   $73.55   $73.50  
  Purchase #3 $92.78   13.134%   $104.9657   $104.97   $104.95   $105.00  
  Purchase #4 $52.83   11.597%   $58.9567   $58.96   $58.95   $59.00  
  Purchase #5 $124.42   8.650%   $135.1823   $135.18   $135.20   $135.20  
  Purchase #6 $236.44   11.163%   $262.8338   $262.83   $262.85   $262.80  
  Purchase #7 $231.40   8.375%   $250.7798   $250.78   $250.80   $250.80  
  7 purchase totals = $1,021.08       $1,129.9842   $1,129.99   $1,130.05   $1,130.00