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 $153.81   7.291%   $165.0243   $165.02   $165.00   $165.00  
  Purchase #2 $236.41   9.852%   $259.7011   $259.70   $259.70   $259.70  
  Purchase #3 $234.74   3.170%   $242.1813   $242.18   $242.20   $242.20  
  Purchase #4 $149.50   12.122%   $167.6224   $167.62   $167.60   $167.60  
  Purchase #5 $215.77   4.179%   $224.787   $224.79   $224.80   $224.80  
  Purchase #6 $109.80   7.388%   $117.912   $117.91   $117.90   $117.90  
  Purchase #7 $89.48   12.613%   $100.7661   $100.77   $100.75   $100.80  
  7 purchase totals = $1,189.51       $1,277.9942   $1,277.99   $1,277.95   $1,278.00