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 $48.41   5.222%   $50.938   $50.94   $50.95   $50.90  
  Purchase #2 $126.47   4.204%   $131.7868   $131.79   $131.80   $131.80  
  Purchase #3 $57.33   13.767%   $65.2226   $65.22   $65.20   $65.20  
  Purchase #4 $131.79   9.542%   $144.3654   $144.37   $144.35   $144.40  
  Purchase #5 $154.75   4.465%   $161.6596   $161.66   $161.65   $161.70  
  Purchase #6 $206.61   6.524%   $220.0892   $220.09   $220.10   $220.10  
  Purchase #7 $54.64   9.794%   $59.9914   $59.99   $60.00   $60.00  
  7 purchase totals = $780.00       $834.0530   $834.06   $834.05   $834.10