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 $247.59   7.571%   $266.335   $266.34   $266.35   $266.30  
  Purchase #2 $21.88   11.253%   $24.3422   $24.34   $24.35   $24.30  
  Purchase #3 $21.72   12.837%   $24.5082   $24.51   $24.50   $24.50  
  Purchase #4 $220.78   13.564%   $250.7266   $250.73   $250.75   $250.70  
  Purchase #5 $41.54   4.866%   $43.5613   $43.56   $43.55   $43.60  
  Purchase #6 $54.76   11.268%   $60.9304   $60.93   $60.95   $60.90  
  Purchase #7 $88.94   5.172%   $93.54   $93.54   $93.55   $93.50  
  7 purchase totals = $697.21       $763.9437   $763.95   $764.00   $763.80