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 $228.67   13.566%   $259.6914   $259.69   $259.70   $259.70  
  Purchase #2 $162.58   12.399%   $182.7383   $182.74   $182.75   $182.70  
  Purchase #3 $103.69   4.646%   $108.5074   $108.51   $108.50   $108.50  
  Purchase #4 $142.72   4.511%   $149.1581   $149.16   $149.15   $149.20  
  Purchase #5 $44.47   9.436%   $48.6662   $48.67   $48.65   $48.70  
  Purchase #6 $218.41   8.426%   $236.8132   $236.81   $236.80   $236.80  
  Purchase #7 $95.67   4.717%   $100.1828   $100.18   $100.20   $100.20  
  7 purchase totals = $996.21       $1,085.7574   $1,085.76   $1,085.75   $1,085.80