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 $58.53   3.822%   $60.767   $60.77   $60.75   $60.80  
  Purchase #2 $22.36   3.681%   $23.1831   $23.18   $23.20   $23.20  
  Purchase #3 $183.68   10.406%   $202.7937   $202.79   $202.80   $202.80  
  Purchase #4 $20.76   9.277%   $22.6859   $22.69   $22.70   $22.70  
  Purchase #5 $104.37   5.132%   $109.7263   $109.73   $109.75   $109.70  
  Purchase #6 $89.33   3.418%   $92.3833   $92.38   $92.40   $92.40  
  Purchase #7 $178.40   8.394%   $193.3749   $193.37   $193.35   $193.40  
  7 purchase totals = $657.43       $704.9142   $704.91   $704.95   $705.00