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 $92.84   11.835%   $103.8276   $103.83   $103.85   $103.80  
  Purchase #2 $168.61   9.625%   $184.8387   $184.84   $184.85   $184.80  
  Purchase #3 $243.39   9.468%   $266.4342   $266.43   $266.45   $266.40  
  Purchase #4 $16.74   13.525%   $19.0041   $19.00   $19.00   $19.00  
  Purchase #5 $90.76   9.210%   $99.119   $99.12   $99.10   $99.10  
  Purchase #6 $131.69   11.629%   $147.0042   $147.00   $147.00   $147.00  
  Purchase #7 $44.70   10.682%   $49.4749   $49.47   $49.45   $49.50  
  7 purchase totals = $788.73       $869.7027   $869.69   $869.70   $869.60