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 $49.67   8.684%   $53.9833   $53.98   $54.00   $54.00  
  Purchase #2 $124.28   6.771%   $132.695   $132.70   $132.70   $132.70  
  Purchase #3 $92.36   11.694%   $103.1606   $103.16   $103.15   $103.20  
  Purchase #4 $187.46   4.518%   $195.9294   $195.93   $195.95   $195.90  
  Purchase #5 $44.48   8.250%   $48.1496   $48.15   $48.15   $48.10  
  Purchase #6 $240.42   13.726%   $273.42   $273.42   $273.40   $273.40  
  Purchase #7 $194.28   12.701%   $218.9555   $218.96   $218.95   $219.00  
  7 purchase totals = $932.95       $1,026.2934   $1,026.30   $1,026.30   $1,026.30