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 $115.28   8.180%   $124.7099   $124.71   $124.70   $124.70  
  Purchase #2 $238.38   5.424%   $251.3097   $251.31   $251.30   $251.30  
  Purchase #3 $30.51   5.777%   $32.2726   $32.27   $32.25   $32.30  
  Purchase #4 $143.87   13.291%   $162.9918   $162.99   $163.00   $163.00  
  Purchase #5 $41.26   7.601%   $44.3962   $44.40   $44.40   $44.40  
  Purchase #6 $129.43   13.698%   $147.1593   $147.16   $147.15   $147.20  
  Purchase #7 $176.36   8.708%   $191.7174   $191.72   $191.70   $191.70  
  7 purchase totals = $875.09       $954.5569   $954.56   $954.50   $954.60