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 $59.94   13.177%   $67.8383   $67.84   $67.85   $67.80  
  Purchase #2 $228.61   7.659%   $246.1192   $246.12   $246.10   $246.10  
  Purchase #3 $201.83   7.336%   $216.6362   $216.64   $216.65   $216.60  
  Purchase #4 $29.83   8.259%   $32.2937   $32.29   $32.30   $32.30  
  Purchase #5 $166.93   11.328%   $185.8398   $185.84   $185.85   $185.80  
  Purchase #6 $249.78   5.561%   $263.6703   $263.67   $263.65   $263.70  
  Purchase #7 $226.75   4.330%   $236.5683   $236.57   $236.55   $236.60  
  7 purchase totals = $1,163.67       $1,248.9658   $1,248.97   $1,248.95   $1,248.90