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 $38.50   11.784%   $43.0368   $43.04   $43.05   $43.00  
  Purchase #2 $250.85   9.849%   $275.5562   $275.56   $275.55   $275.60  
  Purchase #3 $140.74   12.629%   $158.5141   $158.51   $158.50   $158.50  
  Purchase #4 $35.73   6.420%   $38.0239   $38.02   $38.00   $38.00  
  Purchase #5 $55.96   5.109%   $58.819   $58.82   $58.80   $58.80  
  Purchase #6 $176.72   3.126%   $182.2443   $182.24   $182.25   $182.20  
  Purchase #7 $24.69   5.292%   $25.9966   $26.00   $26.00   $26.00  
  7 purchase totals = $723.19       $782.1909   $782.19   $782.15   $782.10