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 $185.75   8.158%   $200.9035   $200.90   $200.90   $200.90  
  Purchase #2 $213.72   11.185%   $237.6246   $237.62   $237.60   $237.60  
  Purchase #3 $86.54   13.774%   $98.46   $98.46   $98.45   $98.50  
  Purchase #4 $228.49   8.693%   $248.3526   $248.35   $248.35   $248.40  
  Purchase #5 $55.79   7.245%   $59.832   $59.83   $59.85   $59.80  
  Purchase #6 $195.45   9.607%   $214.2269   $214.23   $214.25   $214.20  
  Purchase #7 $183.45   6.173%   $194.7744   $194.77   $194.75   $194.80  
  7 purchase totals = $1,149.19       $1,254.1740   $1,254.16   $1,254.15   $1,254.20