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 $195.85   6.121%   $207.838   $207.84   $207.85   $207.80  
  Purchase #2 $180.81   11.503%   $201.6086   $201.61   $201.60   $201.60  
  Purchase #3 $119.99   13.144%   $135.7615   $135.76   $135.75   $135.80  
  Purchase #4 $72.63   4.557%   $75.9397   $75.94   $75.95   $75.90  
  Purchase #5 $40.33   10.114%   $44.409   $44.41   $44.40   $44.40  
  Purchase #6 $58.72   11.267%   $65.336   $65.34   $65.35   $65.30  
  Purchase #7 $40.40   3.493%   $41.8112   $41.81   $41.80   $41.80  
  7 purchase totals = $708.73       $772.7040   $772.71   $772.70   $772.60