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 $32.96   11.652%   $36.8005   $36.80   $36.80   $36.80  
  Purchase #2 $219.97   3.457%   $227.5744   $227.57   $227.55   $227.60  
  Purchase #3 $192.78   3.692%   $199.8974   $199.90   $199.90   $199.90  
  Purchase #4 $101.65   9.452%   $111.258   $111.26   $111.25   $111.30  
  Purchase #5 $244.93   11.246%   $272.4748   $272.47   $272.45   $272.50  
  Purchase #6 $41.98   5.627%   $44.3422   $44.34   $44.35   $44.30  
  Purchase #7 $161.54   10.277%   $178.1415   $178.14   $178.15   $178.10  
  7 purchase totals = $995.81       $1,070.4888   $1,070.48   $1,070.45   $1,070.50