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 $120.66   11.694%   $134.77   $134.77   $134.75   $134.80  
  Purchase #2 $184.33   9.456%   $201.7602   $201.76   $201.75   $201.80  
  Purchase #3 $24.42   8.160%   $26.4127   $26.41   $26.40   $26.40  
  Purchase #4 $23.85   11.162%   $26.5121   $26.51   $26.50   $26.50  
  Purchase #5 $247.82   4.687%   $259.4353   $259.44   $259.45   $259.40  
  Purchase #6 $178.36   4.267%   $185.9706   $185.97   $185.95   $186.00  
  Purchase #7 $103.35   8.332%   $111.9611   $111.96   $111.95   $112.00  
  7 purchase totals = $882.79       $946.8220   $946.82   $946.75   $946.90