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 $167.58   5.378%   $176.5925   $176.59   $176.60   $176.60  
  Purchase #2 $55.42   4.159%   $57.7249   $57.72   $57.70   $57.70  
  Purchase #3 $229.63   6.342%   $244.1931   $244.19   $244.20   $244.20  
  Purchase #4 $32.27   9.486%   $35.3311   $35.33   $35.35   $35.30  
  Purchase #5 $203.70   13.607%   $231.4175   $231.42   $231.40   $231.40  
  Purchase #6 $142.99   7.481%   $153.6871   $153.69   $153.70   $153.70  
  Purchase #7 $153.36   9.403%   $167.7804   $167.78   $167.80   $167.80  
  7 purchase totals = $984.95       $1,066.7266   $1,066.72   $1,066.75   $1,066.70