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 $182.32   13.685%   $207.2705   $207.27   $207.25   $207.30  
  Purchase #2 $220.83   3.621%   $228.8263   $228.83   $228.85   $228.80  
  Purchase #3 $197.30   10.315%   $217.6515   $217.65   $217.65   $217.70  
  Purchase #4 $106.78   9.389%   $116.8056   $116.81   $116.80   $116.80  
  Purchase #5 $23.55   8.159%   $25.4714   $25.47   $25.45   $25.50  
  Purchase #6 $90.71   6.485%   $96.5925   $96.59   $96.60   $96.60  
  Purchase #7 $58.77   9.230%   $64.1945   $64.19   $64.20   $64.20  
  7 purchase totals = $880.26       $956.8123   $956.81   $956.80   $956.90