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 $249.47   7.703%   $268.6867   $268.69   $268.70   $268.70  
  Purchase #2 $202.33   4.751%   $211.9427   $211.94   $211.95   $211.90  
  Purchase #3 $179.28   3.128%   $184.8879   $184.89   $184.90   $184.90  
  Purchase #4 $54.56   5.564%   $57.5957   $57.60   $57.60   $57.60  
  Purchase #5 $122.84   6.801%   $131.1943   $131.19   $131.20   $131.20  
  Purchase #6 $202.83   7.681%   $218.4094   $218.41   $218.40   $218.40  
  Purchase #7 $239.49   8.639%   $260.1795   $260.18   $260.20   $260.20  
  7 purchase totals = $1,250.80       $1,332.8962   $1,332.90   $1,332.95   $1,332.90