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 $177.50   13.379%   $201.2477   $201.25   $201.25   $201.20  
  Purchase #2 $55.79   10.656%   $61.735   $61.74   $61.75   $61.70  
  Purchase #3 $100.79   5.111%   $105.9414   $105.94   $105.95   $105.90  
  Purchase #4 $69.71   5.565%   $73.5894   $73.59   $73.60   $73.60  
  Purchase #5 $82.46   6.787%   $88.0566   $88.06   $88.05   $88.10  
  Purchase #6 $123.81   4.528%   $129.4161   $129.42   $129.40   $129.40  
  Purchase #7 $126.47   11.697%   $141.2632   $141.26   $141.25   $141.30  
  7 purchase totals = $736.53       $801.2494   $801.26   $801.25   $801.20