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 $120.47   9.585%   $132.017   $132.02   $132.00   $132.00  
  Purchase #2 $194.73   3.261%   $201.0801   $201.08   $201.10   $201.10  
  Purchase #3 $208.61   5.223%   $219.5057   $219.51   $219.50   $219.50  
  Purchase #4 $68.56   7.608%   $73.776   $73.78   $73.80   $73.80  
  Purchase #5 $141.95   10.216%   $156.4516   $156.45   $156.45   $156.50  
  Purchase #6 $65.34   3.306%   $67.5001   $67.50   $67.50   $67.50  
  Purchase #7 $14.45   11.619%   $16.1289   $16.13   $16.15   $16.10  
  7 purchase totals = $814.11       $866.4594   $866.47   $866.50   $866.50