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 $245.87   11.356%   $273.791   $273.79   $273.80   $273.80  
  Purchase #2 $182.47   9.815%   $200.3794   $200.38   $200.40   $200.40  
  Purchase #3 $71.48   7.324%   $76.7152   $76.72   $76.70   $76.70  
  Purchase #4 $24.71   5.675%   $26.1123   $26.11   $26.10   $26.10  
  Purchase #5 $195.47   13.553%   $221.962   $221.96   $221.95   $222.00  
  Purchase #6 $210.59   7.593%   $226.5801   $226.58   $226.60   $226.60  
  Purchase #7 $132.46   3.654%   $137.3001   $137.30   $137.30   $137.30  
  7 purchase totals = $1,063.05       $1,162.8401   $1,162.84   $1,162.85   $1,162.90