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 $24.50   5.132%   $25.7573   $25.76   $25.75   $25.80  
  Purchase #2 $156.28   6.874%   $167.0227   $167.02   $167.00   $167.00  
  Purchase #3 $26.70   4.116%   $27.799   $27.80   $27.80   $27.80  
  Purchase #4 $210.42   9.533%   $230.4793   $230.48   $230.50   $230.50  
  Purchase #5 $121.74   11.344%   $135.5502   $135.55   $135.55   $135.60  
  Purchase #6 $57.77   13.238%   $65.4176   $65.42   $65.40   $65.40  
  Purchase #7 $80.27   10.828%   $88.9616   $88.96   $88.95   $89.00  
  7 purchase totals = $677.68       $740.9877   $740.99   $740.95   $741.10