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 $180.98   8.874%   $197.0402   $197.04   $197.05   $197.00  
  Purchase #2 $250.42   10.829%   $277.538   $277.54   $277.55   $277.50  
  Purchase #3 $44.72   11.218%   $49.7367   $49.74   $49.75   $49.70  
  Purchase #4 $83.99   10.275%   $92.62   $92.62   $92.60   $92.60  
  Purchase #5 $211.80   13.487%   $240.3655   $240.37   $240.35   $240.40  
  Purchase #6 $19.92   6.339%   $21.1827   $21.18   $21.20   $21.20  
  Purchase #7 $107.86   9.276%   $117.8651   $117.87   $117.85   $117.90  
  7 purchase totals = $899.69       $996.3482   $996.36   $996.35   $996.30