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 $91.71   6.780%   $97.9279   $97.93   $97.95   $97.90  
  Purchase #2 $235.57   13.155%   $266.5592   $266.56   $266.55   $266.60  
  Purchase #3 $34.33   10.806%   $38.0397   $38.04   $38.05   $38.00  
  Purchase #4 $66.49   5.650%   $70.2467   $70.25   $70.25   $70.20  
  Purchase #5 $52.30   3.864%   $54.3209   $54.32   $54.30   $54.30  
  Purchase #6 $21.42   8.180%   $23.1722   $23.17   $23.15   $23.20  
  Purchase #7 $249.64   13.150%   $282.4677   $282.47   $282.45   $282.50  
  7 purchase totals = $751.46       $832.7343   $832.74   $832.70   $832.70