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 $198.30   6.788%   $211.7606   $211.76   $211.75   $211.80  
  Purchase #2 $53.90   13.148%   $60.9868   $60.99   $61.00   $61.00  
  Purchase #3 $104.82   8.253%   $113.4708   $113.47   $113.45   $113.50  
  Purchase #4 $142.66   9.523%   $156.2455   $156.25   $156.25   $156.20  
  Purchase #5 $72.91   5.236%   $76.7276   $76.73   $76.75   $76.70  
  Purchase #6 $225.43   12.613%   $253.8635   $253.86   $253.85   $253.90  
  Purchase #7 $53.97   4.375%   $56.3312   $56.33   $56.35   $56.30  
  7 purchase totals = $851.99       $929.3860   $929.39   $929.40   $929.40