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 $30.41   5.453%   $32.0683   $32.07   $32.05   $32.10  
  Purchase #2 $204.55   11.507%   $228.0876   $228.09   $228.10   $228.10  
  Purchase #3 $128.26   3.360%   $132.5695   $132.57   $132.55   $132.60  
  Purchase #4 $233.93   10.683%   $258.9207   $258.92   $258.90   $258.90  
  Purchase #5 $8.73   13.666%   $9.923   $9.92   $9.90   $9.90  
  Purchase #6 $160.45   13.768%   $182.5408   $182.54   $182.55   $182.50  
  Purchase #7 $156.82   13.308%   $177.6896   $177.69   $177.70   $177.70  
  7 purchase totals = $923.15       $1,021.7995   $1,021.80   $1,021.75   $1,021.80