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 $68.49   13.264%   $77.5745   $77.57   $77.55   $77.60  
  Purchase #2 $178.28   9.275%   $194.8155   $194.82   $194.80   $194.80  
  Purchase #3 $245.34   10.256%   $270.5021   $270.50   $270.50   $270.50  
  Purchase #4 $111.97   13.430%   $127.0076   $127.01   $127.00   $127.00  
  Purchase #5 $88.74   10.607%   $98.1527   $98.15   $98.15   $98.20  
  Purchase #6 $41.95   5.768%   $44.3697   $44.37   $44.35   $44.40  
  Purchase #7 $156.66   10.253%   $172.7223   $172.72   $172.70   $172.70  
  7 purchase totals = $891.43       $985.1444   $985.14   $985.05   $985.20