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 $87.44   8.821%   $95.1531   $95.15   $95.15   $95.20  
  Purchase #2 $222.93   6.651%   $237.7571   $237.76   $237.75   $237.80  
  Purchase #3 $120.41   8.132%   $130.2017   $130.20   $130.20   $130.20  
  Purchase #4 $238.67   4.520%   $249.4579   $249.46   $249.45   $249.50  
  Purchase #5 $54.65   8.223%   $59.1439   $59.14   $59.15   $59.10  
  Purchase #6 $180.70   10.591%   $199.8379   $199.84   $199.85   $199.80  
  Purchase #7 $35.82   4.651%   $37.486   $37.49   $37.50   $37.50  
  7 purchase totals = $940.62       $1,009.0376   $1,009.04   $1,009.05   $1,009.10