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 $208.88   6.743%   $222.9648   $222.96   $222.95   $223.00  
  Purchase #2 $30.43   10.466%   $33.6148   $33.61   $33.60   $33.60  
  Purchase #3 $74.75   4.226%   $77.9089   $77.91   $77.90   $77.90  
  Purchase #4 $212.56   9.601%   $232.9679   $232.97   $232.95   $233.00  
  Purchase #5 $124.68   5.783%   $131.8902   $131.89   $131.90   $131.90  
  Purchase #6 $204.54   8.486%   $221.8973   $221.90   $221.90   $221.90  
  Purchase #7 $25.36   6.673%   $27.0523   $27.05   $27.05   $27.10  
  7 purchase totals = $881.20       $948.2962   $948.29   $948.25   $948.40