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 $117.74   5.795%   $124.563   $124.56   $124.55   $124.60  
  Purchase #2 $50.94   6.210%   $54.1034   $54.10   $54.10   $54.10  
  Purchase #3 $51.94   13.319%   $58.8579   $58.86   $58.85   $58.90  
  Purchase #4 $249.84   3.837%   $259.4264   $259.43   $259.45   $259.40  
  Purchase #5 $7.99   7.449%   $8.5852   $8.59   $8.60   $8.60  
  Purchase #6 $75.93   3.413%   $78.5215   $78.52   $78.50   $78.50  
  Purchase #7 $153.48   11.617%   $171.3098   $171.31   $171.30   $171.30  
  7 purchase totals = $707.86       $755.3672   $755.37   $755.35   $755.40