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 $80.29   5.847%   $84.9846   $84.98   $85.00   $85.00  
  Purchase #2 $183.88   5.725%   $194.4071   $194.41   $194.40   $194.40  
  Purchase #3 $50.44   5.493%   $53.2107   $53.21   $53.20   $53.20  
  Purchase #4 $100.95   3.209%   $104.1895   $104.19   $104.20   $104.20  
  Purchase #5 $224.96   7.526%   $241.8905   $241.89   $241.90   $241.90  
  Purchase #6 $185.80   6.706%   $198.2597   $198.26   $198.25   $198.30  
  Purchase #7 $68.43   6.803%   $73.0853   $73.09   $73.10   $73.10  
  7 purchase totals = $894.75       $950.0274   $950.03   $950.05   $950.10