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 $249.54   5.715%   $263.8012   $263.80   $263.80   $263.80  
  Purchase #2 $167.58   10.422%   $185.0452   $185.05   $185.05   $185.00  
  Purchase #3 $124.70   8.178%   $134.898   $134.90   $134.90   $134.90  
  Purchase #4 $52.77   7.289%   $56.6164   $56.62   $56.60   $56.60  
  Purchase #5 $81.99   11.298%   $91.2532   $91.25   $91.25   $91.30  
  Purchase #6 $216.26   13.193%   $244.7912   $244.79   $244.80   $244.80  
  Purchase #7 $108.63   10.811%   $120.374   $120.37   $120.35   $120.40  
  7 purchase totals = $1,001.47       $1,096.7792   $1,096.78   $1,096.75   $1,096.80