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 $208.31   8.145%   $225.2768   $225.28   $225.30   $225.30  
  Purchase #2 $111.94   12.293%   $125.7008   $125.70   $125.70   $125.70  
  Purchase #3 $99.98   6.775%   $106.7536   $106.75   $106.75   $106.80  
  Purchase #4 $185.87   4.472%   $194.1821   $194.18   $194.20   $194.20  
  Purchase #5 $168.65   7.142%   $180.695   $180.70   $180.70   $180.70  
  Purchase #6 $171.61   8.855%   $186.8061   $186.81   $186.80   $186.80  
  Purchase #7 $166.34   13.239%   $188.3618   $188.36   $188.35   $188.40  
  7 purchase totals = $1,112.70       $1,207.7762   $1,207.78   $1,207.80   $1,207.90