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 $195.37   6.232%   $207.5455   $207.55   $207.55   $207.50  
  Purchase #2 $120.56   4.633%   $126.1455   $126.15   $126.15   $126.10  
  Purchase #3 $178.79   4.432%   $186.714   $186.71   $186.70   $186.70  
  Purchase #4 $243.39   10.534%   $269.0287   $269.03   $269.05   $269.00  
  Purchase #5 $155.65   12.257%   $174.728   $174.73   $174.75   $174.70  
  Purchase #6 $140.55   11.440%   $156.6289   $156.63   $156.65   $156.60  
  Purchase #7 $209.62   9.481%   $229.4941   $229.49   $229.50   $229.50  
  7 purchase totals = $1,243.93       $1,350.2847   $1,350.29   $1,350.35   $1,350.10