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 $60.82   13.602%   $69.0927   $69.09   $69.10   $69.10  
  Purchase #2 $119.98   8.610%   $130.3103   $130.31   $130.30   $130.30  
  Purchase #3 $29.45   8.124%   $31.8425   $31.84   $31.85   $31.80  
  Purchase #4 $102.50   3.824%   $106.4196   $106.42   $106.40   $106.40  
  Purchase #5 $64.42   5.493%   $67.9586   $67.96   $67.95   $68.00  
  Purchase #6 $71.73   3.438%   $74.1961   $74.20   $74.20   $74.20  
  Purchase #7 $56.69   8.468%   $61.4905   $61.49   $61.50   $61.50  
  7 purchase totals = $505.59       $541.3103   $541.31   $541.30   $541.30