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 $91.64   13.173%   $103.7117   $103.71   $103.70   $103.70  
  Purchase #2 $233.83   11.770%   $261.3518   $261.35   $261.35   $261.40  
  Purchase #3 $117.84   9.309%   $128.8097   $128.81   $128.80   $128.80  
  Purchase #4 $40.32   6.351%   $42.8807   $42.88   $42.90   $42.90  
  Purchase #5 $201.64   5.136%   $211.9962   $212.00   $212.00   $212.00  
  Purchase #6 $132.83   8.203%   $143.726   $143.73   $143.75   $143.70  
  Purchase #7 $250.38   3.282%   $258.5975   $258.60   $258.60   $258.60  
  7 purchase totals = $1,068.48       $1,151.0736   $1,151.08   $1,151.10   $1,151.10