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 $208.96   11.326%   $232.6268   $232.63   $232.65   $232.60  
  Purchase #2 $116.95   11.144%   $129.9829   $129.98   $130.00   $130.00  
  Purchase #3 $24.30   12.275%   $27.2828   $27.28   $27.30   $27.30  
  Purchase #4 $160.31   6.163%   $170.1899   $170.19   $170.20   $170.20  
  Purchase #5 $107.85   7.564%   $116.0078   $116.01   $116.00   $116.00  
  Purchase #6 $122.33   6.398%   $130.1567   $130.16   $130.15   $130.20  
  Purchase #7 $128.64   6.118%   $136.5102   $136.51   $136.50   $136.50  
  7 purchase totals = $869.34       $942.7571   $942.76   $942.80   $942.80