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 $238.90   6.197%   $253.7046   $253.70   $253.70   $253.70  
  Purchase #2 $14.79   6.700%   $15.7809   $15.78   $15.80   $15.80  
  Purchase #3 $64.30   13.705%   $73.1123   $73.11   $73.10   $73.10  
  Purchase #4 $26.68   9.466%   $29.2055   $29.21   $29.20   $29.20  
  Purchase #5 $164.88   8.836%   $179.4488   $179.45   $179.45   $179.40  
  Purchase #6 $117.40   11.834%   $131.2931   $131.29   $131.30   $131.30  
  Purchase #7 $97.73   6.455%   $104.0385   $104.04   $104.05   $104.00  
  7 purchase totals = $724.68       $786.5837   $786.58   $786.60   $786.50