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 $63.36   8.804%   $68.9382   $68.94   $68.95   $68.90  
  Purchase #2 $68.44   6.546%   $72.9201   $72.92   $72.90   $72.90  
  Purchase #3 $248.84   13.541%   $282.5354   $282.54   $282.55   $282.50  
  Purchase #4 $139.74   10.433%   $154.3191   $154.32   $154.30   $154.30  
  Purchase #5 $159.28   10.648%   $176.2401   $176.24   $176.25   $176.20  
  Purchase #6 $211.43   5.771%   $223.6316   $223.63   $223.65   $223.60  
  Purchase #7 $22.93   9.538%   $25.1171   $25.12   $25.10   $25.10  
  7 purchase totals = $914.02       $1,003.7016   $1,003.71   $1,003.70   $1,003.50