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 $38.74   13.683%   $44.0408   $44.04   $44.05   $44.00  
  Purchase #2 $209.83   8.666%   $228.0139   $228.01   $228.00   $228.00  
  Purchase #3 $63.38   4.580%   $66.2828   $66.28   $66.30   $66.30  
  Purchase #4 $77.39   8.413%   $83.9008   $83.90   $83.90   $83.90  
  Purchase #5 $156.48   3.821%   $162.4591   $162.46   $162.45   $162.50  
  Purchase #6 $112.64   9.700%   $123.5661   $123.57   $123.55   $123.60  
  Purchase #7 $43.77   8.536%   $47.5062   $47.51   $47.50   $47.50  
  7 purchase totals = $702.23       $755.7697   $755.77   $755.75   $755.80