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 $87.53   9.766%   $96.0782   $96.08   $96.10   $96.10  
  Purchase #2 $240.44   12.198%   $269.7689   $269.77   $269.75   $269.80  
  Purchase #3 $63.49   8.306%   $68.7635   $68.76   $68.75   $68.80  
  Purchase #4 $36.26   4.560%   $37.9135   $37.91   $37.90   $37.90  
  Purchase #5 $133.62   4.301%   $139.367   $139.37   $139.35   $139.40  
  Purchase #6 $126.56   6.548%   $134.8471   $134.85   $134.85   $134.80  
  Purchase #7 $27.49   7.326%   $29.5039   $29.50   $29.50   $29.50  
  7 purchase totals = $715.39       $776.2421   $776.24   $776.20   $776.30