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 $92.45   3.579%   $95.7588   $95.76   $95.75   $95.80  
  Purchase #2 $249.74   13.760%   $284.1042   $284.10   $284.10   $284.10  
  Purchase #3 $84.93   13.838%   $96.6826   $96.68   $96.70   $96.70  
  Purchase #4 $90.54   3.196%   $93.4337   $93.43   $93.45   $93.40  
  Purchase #5 $97.99   9.133%   $106.9394   $106.94   $106.95   $106.90  
  Purchase #6 $93.48   10.537%   $103.33   $103.33   $103.35   $103.30  
  Purchase #7 $214.43   11.502%   $239.0937   $239.09   $239.10   $239.10  
  7 purchase totals = $923.56       $1,019.3424   $1,019.33   $1,019.40   $1,019.30