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 $59.81   4.729%   $62.6384   $62.64   $62.65   $62.60  
  Purchase #2 $12.62   9.253%   $13.7877   $13.79   $13.80   $13.80  
  Purchase #3 $156.31   12.599%   $176.0035   $176.00   $176.00   $176.00  
  Purchase #4 $68.36   12.644%   $77.0034   $77.00   $77.00   $77.00  
  Purchase #5 $83.85   9.235%   $91.5935   $91.59   $91.60   $91.60  
  Purchase #6 $133.70   9.391%   $146.2558   $146.26   $146.25   $146.30  
  Purchase #7 $240.28   3.749%   $249.2881   $249.29   $249.30   $249.30  
  7 purchase totals = $754.93       $816.5704   $816.57   $816.60   $816.60