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 $101.62   8.775%   $110.5372   $110.54   $110.55   $110.50  
  Purchase #2 $177.87   8.862%   $193.6328   $193.63   $193.65   $193.60  
  Purchase #3 $106.90   11.373%   $119.0577   $119.06   $119.05   $119.10  
  Purchase #4 $64.74   10.633%   $71.6238   $71.62   $71.60   $71.60  
  Purchase #5 $191.28   8.345%   $207.2423   $207.24   $207.25   $207.20  
  Purchase #6 $180.53   6.734%   $192.6869   $192.69   $192.70   $192.70  
  Purchase #7 $50.56   8.535%   $54.8753   $54.88   $54.90   $54.90  
  7 purchase totals = $873.50       $949.6560   $949.66   $949.70   $949.60