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 $213.69   5.670%   $225.8062   $225.81   $225.80   $225.80  
  Purchase #2 $192.29   12.821%   $216.9435   $216.94   $216.95   $216.90  
  Purchase #3 $104.33   12.150%   $117.0061   $117.01   $117.00   $117.00  
  Purchase #4 $240.95   6.674%   $257.031   $257.03   $257.05   $257.00  
  Purchase #5 $214.60   11.171%   $238.573   $238.57   $238.55   $238.60  
  Purchase #6 $109.91   3.210%   $113.4381   $113.44   $113.45   $113.40  
  Purchase #7 $92.95   7.119%   $99.5671   $99.57   $99.55   $99.60  
  7 purchase totals = $1,168.72       $1,268.3650   $1,268.37   $1,268.35   $1,268.30