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 $198.39   12.273%   $222.7384   $222.74   $222.75   $222.70  
  Purchase #2 $215.44   4.509%   $225.1542   $225.15   $225.15   $225.20  
  Purchase #3 $47.98   13.417%   $54.4175   $54.42   $54.40   $54.40  
  Purchase #4 $246.81   6.801%   $263.5955   $263.60   $263.60   $263.60  
  Purchase #5 $160.73   8.220%   $173.942   $173.94   $173.95   $173.90  
  Purchase #6 $217.57   11.326%   $242.212   $242.21   $242.20   $242.20  
  Purchase #7 $220.55   6.466%   $234.8108   $234.81   $234.80   $234.80  
  7 purchase totals = $1,307.47       $1,416.8704   $1,416.87   $1,416.85   $1,416.80