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 $240.96   10.429%   $266.0897   $266.09   $266.10   $266.10  
  Purchase #2 $239.32   5.134%   $251.6067   $251.61   $251.60   $251.60  
  Purchase #3 $34.44   13.511%   $39.0932   $39.09   $39.10   $39.10  
  Purchase #4 $98.36   3.676%   $101.9757   $101.98   $102.00   $102.00  
  Purchase #5 $197.35   6.646%   $210.4659   $210.47   $210.45   $210.50  
  Purchase #6 $170.55   9.494%   $186.742   $186.74   $186.75   $186.70  
  Purchase #7 $155.93   5.297%   $164.1896   $164.19   $164.20   $164.20  
  7 purchase totals = $1,136.91       $1,220.1628   $1,220.17   $1,220.20   $1,220.20