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 $238.62   11.480%   $266.0136   $266.01   $266.00   $266.00  
  Purchase #2 $66.52   9.683%   $72.9611   $72.96   $72.95   $73.00  
  Purchase #3 $28.77   10.669%   $31.8395   $31.84   $31.85   $31.80  
  Purchase #4 $104.49   3.548%   $108.1973   $108.20   $108.20   $108.20  
  Purchase #5 $241.38   7.547%   $259.5969   $259.60   $259.60   $259.60  
  Purchase #6 $231.96   5.473%   $244.6552   $244.66   $244.65   $244.70  
  Purchase #7 $207.43   4.391%   $216.5383   $216.54   $216.55   $216.50  
  7 purchase totals = $1,119.17       $1,199.8019   $1,199.81   $1,199.80   $1,199.80