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 $207.63   8.519%   $225.318   $225.32   $225.30   $225.30  
  Purchase #2 $176.66   7.527%   $189.9572   $189.96   $189.95   $190.00  
  Purchase #3 $44.36   6.236%   $47.1263   $47.13   $47.15   $47.10  
  Purchase #4 $203.93   10.165%   $224.6595   $224.66   $224.65   $224.70  
  Purchase #5 $11.90   7.200%   $12.7568   $12.76   $12.75   $12.80  
  Purchase #6 $218.48   13.133%   $247.173   $247.17   $247.15   $247.20  
  Purchase #7 $158.27   8.246%   $171.3209   $171.32   $171.30   $171.30  
  7 purchase totals = $1,021.23       $1,118.3117   $1,118.32   $1,118.25   $1,118.40