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 $67.82   11.531%   $75.6403   $75.64   $75.65   $75.60  
  Purchase #2 $241.36   5.247%   $254.0242   $254.02   $254.00   $254.00  
  Purchase #3 $190.28   6.384%   $202.4275   $202.43   $202.45   $202.40  
  Purchase #4 $235.69   13.253%   $266.926   $266.93   $266.95   $266.90  
  Purchase #5 $60.38   13.494%   $68.5277   $68.53   $68.55   $68.50  
  Purchase #6 $90.92   11.613%   $101.4785   $101.48   $101.50   $101.50  
  Purchase #7 $90.49   5.229%   $95.2217   $95.22   $95.20   $95.20  
  7 purchase totals = $976.94       $1,064.2459   $1,064.25   $1,064.30   $1,064.10