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 $171.25   11.668%   $191.2315   $191.23   $191.25   $191.20  
  Purchase #2 $113.48   10.739%   $125.6666   $125.67   $125.65   $125.70  
  Purchase #3 $236.66   7.590%   $254.6225   $254.62   $254.60   $254.60  
  Purchase #4 $49.50   5.523%   $52.2339   $52.23   $52.25   $52.20  
  Purchase #5 $162.53   10.371%   $179.386   $179.39   $179.40   $179.40  
  Purchase #6 $175.60   12.138%   $196.9143   $196.91   $196.90   $196.90  
  Purchase #7 $217.79   8.191%   $235.6292   $235.63   $235.65   $235.60  
  7 purchase totals = $1,126.81       $1,235.6840   $1,235.68   $1,235.70   $1,235.60