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 $198.59   3.689%   $205.916   $205.92   $205.90   $205.90  
  Purchase #2 $65.92   3.172%   $68.011   $68.01   $68.00   $68.00  
  Purchase #3 $203.31   5.384%   $214.2562   $214.26   $214.25   $214.30  
  Purchase #4 $238.79   4.246%   $248.929   $248.93   $248.95   $248.90  
  Purchase #5 $151.95   5.117%   $159.7253   $159.73   $159.75   $159.70  
  Purchase #6 $248.89   7.468%   $267.4771   $267.48   $267.50   $267.50  
  Purchase #7 $160.45   11.725%   $179.2628   $179.26   $179.25   $179.30  
  7 purchase totals = $1,267.90       $1,343.5774   $1,343.59   $1,343.60   $1,343.60