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 $83.54   13.382%   $94.7193   $94.72   $94.70   $94.70  
  Purchase #2 $111.86   5.702%   $118.2383   $118.24   $118.25   $118.20  
  Purchase #3 $210.97   5.255%   $222.0565   $222.06   $222.05   $222.10  
  Purchase #4 $90.71   5.749%   $95.9249   $95.92   $95.90   $95.90  
  Purchase #5 $62.52   6.351%   $66.4906   $66.49   $66.50   $66.50  
  Purchase #6 $117.95   12.590%   $132.7999   $132.80   $132.80   $132.80  
  Purchase #7 $163.28   5.619%   $172.4547   $172.45   $172.45   $172.50  
  7 purchase totals = $840.83       $902.6842   $902.68   $902.65   $902.70