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 $217.30   12.448%   $244.3495   $244.35   $244.35   $244.30  
  Purchase #2 $108.39   4.818%   $113.6122   $113.61   $113.60   $113.60  
  Purchase #3 $168.67   3.772%   $175.0322   $175.03   $175.05   $175.00  
  Purchase #4 $182.43   11.597%   $203.5864   $203.59   $203.60   $203.60  
  Purchase #5 $33.78   6.708%   $36.046   $36.05   $36.05   $36.00  
  Purchase #6 $53.53   7.247%   $57.4093   $57.41   $57.40   $57.40  
  Purchase #7 $170.98   13.199%   $193.5477   $193.55   $193.55   $193.50  
  7 purchase totals = $935.08       $1,023.5833   $1,023.59   $1,023.60   $1,023.40