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 $248.76   11.788%   $278.0838   $278.08   $278.10   $278.10  
  Purchase #2 $223.81   5.178%   $235.3989   $235.40   $235.40   $235.40  
  Purchase #3 $24.71   5.151%   $25.9828   $25.98   $26.00   $26.00  
  Purchase #4 $125.55   5.726%   $132.739   $132.74   $132.75   $132.70  
  Purchase #5 $130.49   11.873%   $145.9831   $145.98   $146.00   $146.00  
  Purchase #6 $75.97   8.750%   $82.6174   $82.62   $82.60   $82.60  
  Purchase #7 $120.33   9.266%   $131.4798   $131.48   $131.50   $131.50  
  7 purchase totals = $949.62       $1,032.2848   $1,032.28   $1,032.35   $1,032.30