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 $231.95   4.602%   $242.6243   $242.62   $242.60   $242.60  
  Purchase #2 $14.70   5.682%   $15.5353   $15.54   $15.55   $15.50  
  Purchase #3 $234.55   9.768%   $257.4608   $257.46   $257.45   $257.50  
  Purchase #4 $168.73   9.520%   $184.7931   $184.79   $184.80   $184.80  
  Purchase #5 $169.89   4.397%   $177.3601   $177.36   $177.35   $177.40  
  Purchase #6 $59.58   8.868%   $64.8636   $64.86   $64.85   $64.90  
  Purchase #7 $224.68   3.564%   $232.6876   $232.69   $232.70   $232.70  
  7 purchase totals = $1,104.08       $1,175.3248   $1,175.32   $1,175.30   $1,175.40