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 $95.51   9.248%   $104.3428   $104.34   $104.35   $104.30  
  Purchase #2 $36.96   4.565%   $38.6472   $38.65   $38.65   $38.60  
  Purchase #3 $237.46   11.650%   $265.1241   $265.12   $265.10   $265.10  
  Purchase #4 $82.49   12.263%   $92.6057   $92.61   $92.60   $92.60  
  Purchase #5 $60.80   13.323%   $68.9004   $68.90   $68.90   $68.90  
  Purchase #6 $217.62   5.138%   $228.8013   $228.80   $228.80   $228.80  
  Purchase #7 $178.98   7.664%   $192.697   $192.70   $192.70   $192.70  
  7 purchase totals = $909.82       $991.1185   $991.12   $991.10   $991.00