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 $70.68   7.871%   $76.2432   $76.24   $76.25   $76.20  
  Purchase #2 $211.42   8.338%   $229.0482   $229.05   $229.05   $229.00  
  Purchase #3 $175.38   6.829%   $187.3567   $187.36   $187.35   $187.40  
  Purchase #4 $119.83   4.140%   $124.791   $124.79   $124.80   $124.80  
  Purchase #5 $5.73   5.211%   $6.0286   $6.03   $6.05   $6.00  
  Purchase #6 $245.39   6.801%   $262.079   $262.08   $262.10   $262.10  
  Purchase #7 $154.32   10.737%   $170.8893   $170.89   $170.90   $170.90  
  7 purchase totals = $982.75       $1,056.4360   $1,056.44   $1,056.50   $1,056.40