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 $201.55   3.463%   $208.5297   $208.53   $208.55   $208.50  
  Purchase #2 $170.75   6.574%   $181.9751   $181.98   $182.00   $182.00  
  Purchase #3 $52.58   9.154%   $57.3932   $57.39   $57.40   $57.40  
  Purchase #4 $54.78   3.198%   $56.5319   $56.53   $56.55   $56.50  
  Purchase #5 $64.75   9.609%   $70.9718   $70.97   $70.95   $71.00  
  Purchase #6 $231.75   13.193%   $262.3248   $262.32   $262.30   $262.30  
  Purchase #7 $182.70   11.524%   $203.7543   $203.75   $203.75   $203.80  
  7 purchase totals = $958.86       $1,041.4808   $1,041.47   $1,041.50   $1,041.50