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 $62.93   9.473%   $68.8914   $68.89   $68.90   $68.90  
  Purchase #2 $137.48   8.400%   $149.0283   $149.03   $149.05   $149.00  
  Purchase #3 $202.56   8.462%   $219.7006   $219.70   $219.70   $219.70  
  Purchase #4 $21.55   5.486%   $22.7322   $22.73   $22.75   $22.70  
  Purchase #5 $239.82   4.509%   $250.6335   $250.63   $250.65   $250.60  
  Purchase #6 $234.92   10.460%   $259.4926   $259.49   $259.50   $259.50  
  Purchase #7 $104.68   8.867%   $113.962   $113.96   $113.95   $114.00  
  7 purchase totals = $1,003.94       $1,084.4406   $1,084.43   $1,084.50   $1,084.40