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 $228.36   10.242%   $251.7486   $251.75   $251.75   $251.70  
  Purchase #2 $118.45   8.653%   $128.6995   $128.70   $128.70   $128.70  
  Purchase #3 $174.89   5.497%   $184.5037   $184.50   $184.50   $184.50  
  Purchase #4 $131.30   3.174%   $135.4675   $135.47   $135.45   $135.50  
  Purchase #5 $8.49   12.238%   $9.529   $9.53   $9.55   $9.50  
  Purchase #6 $121.46   3.426%   $125.6212   $125.62   $125.60   $125.60  
  Purchase #7 $179.51   4.186%   $187.0243   $187.02   $187.00   $187.00  
  7 purchase totals = $962.46       $1,022.5938   $1,022.59   $1,022.55   $1,022.50