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 $114.26   5.105%   $120.093   $120.09   $120.10   $120.10  
  Purchase #2 $123.25   10.534%   $136.2332   $136.23   $136.25   $136.20  
  Purchase #3 $167.55   9.315%   $183.1573   $183.16   $183.15   $183.20  
  Purchase #4 $80.49   4.479%   $84.0951   $84.10   $84.10   $84.10  
  Purchase #5 $226.99   4.742%   $237.7539   $237.75   $237.75   $237.80  
  Purchase #6 $228.30   6.407%   $242.9272   $242.93   $242.95   $242.90  
  Purchase #7 $147.42   12.437%   $165.7546   $165.75   $165.75   $165.80  
  7 purchase totals = $1,088.26       $1,170.0143   $1,170.01   $1,170.05   $1,170.10