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 $56.86   5.399%   $59.9299   $59.93   $59.95   $59.90  
  Purchase #2 $245.91   9.538%   $269.3649   $269.36   $269.35   $269.40  
  Purchase #3 $250.54   3.454%   $259.1937   $259.19   $259.20   $259.20  
  Purchase #4 $170.31   6.861%   $181.995   $182.00   $182.00   $182.00  
  Purchase #5 $176.34   10.551%   $194.9456   $194.95   $194.95   $194.90  
  Purchase #6 $63.47   4.817%   $66.5273   $66.53   $66.55   $66.50  
  Purchase #7 $83.64   6.178%   $88.8073   $88.81   $88.80   $88.80  
  7 purchase totals = $1,047.07       $1,120.7637   $1,120.77   $1,120.80   $1,120.70