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 $186.42   8.746%   $202.7243   $202.72   $202.70   $202.70  
  Purchase #2 $177.91   8.833%   $193.6248   $193.62   $193.60   $193.60  
  Purchase #3 $143.67   4.213%   $149.7228   $149.72   $149.70   $149.70  
  Purchase #4 $90.40   9.110%   $98.6354   $98.64   $98.65   $98.60  
  Purchase #5 $232.44   7.762%   $250.482   $250.48   $250.50   $250.50  
  Purchase #6 $43.63   13.479%   $49.5109   $49.51   $49.50   $49.50  
  Purchase #7 $59.78   8.281%   $64.7304   $64.73   $64.75   $64.70  
  7 purchase totals = $934.25       $1,009.4306   $1,009.42   $1,009.40   $1,009.30