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 $162.89   8.484%   $176.7096   $176.71   $176.70   $176.70  
  Purchase #2 $193.93   5.335%   $204.2762   $204.28   $204.30   $204.30  
  Purchase #3 $109.30   5.201%   $114.9847   $114.98   $115.00   $115.00  
  Purchase #4 $167.61   9.480%   $183.4994   $183.50   $183.50   $183.50  
  Purchase #5 $104.39   13.427%   $118.4064   $118.41   $118.40   $118.40  
  Purchase #6 $172.26   7.737%   $185.5878   $185.59   $185.60   $185.60  
  Purchase #7 $34.38   9.723%   $37.7228   $37.72   $37.70   $37.70  
  7 purchase totals = $944.76       $1,021.1869   $1,021.19   $1,021.20   $1,021.20