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 $88.49   7.630%   $95.2418   $95.24   $95.25   $95.20  
  Purchase #2 $155.54   13.874%   $177.1196   $177.12   $177.10   $177.10  
  Purchase #3 $219.48   13.782%   $249.7287   $249.73   $249.75   $249.70  
  Purchase #4 $44.44   4.444%   $46.4149   $46.41   $46.40   $46.40  
  Purchase #5 $116.75   11.680%   $130.3864   $130.39   $130.40   $130.40  
  Purchase #6 $146.31   4.502%   $152.8969   $152.90   $152.90   $152.90  
  Purchase #7 $201.85   13.470%   $229.0392   $229.04   $229.05   $229.00  
  7 purchase totals = $972.86       $1,080.8275   $1,080.83   $1,080.85   $1,080.70