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 $66.65   7.733%   $71.804   $71.80   $71.80   $71.80  
  Purchase #2 $90.76   5.440%   $95.6973   $95.70   $95.70   $95.70  
  Purchase #3 $222.39   11.559%   $248.0961   $248.10   $248.10   $248.10  
  Purchase #4 $42.50   5.815%   $44.9714   $44.97   $44.95   $45.00  
  Purchase #5 $244.75   7.153%   $262.257   $262.26   $262.25   $262.30  
  Purchase #6 $236.93   4.516%   $247.6298   $247.63   $247.65   $247.60  
  Purchase #7 $16.28   9.415%   $17.8128   $17.81   $17.80   $17.80  
  7 purchase totals = $920.26       $988.2684   $988.27   $988.25   $988.30