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 $13.77   8.241%   $14.9048   $14.90   $14.90   $14.90  
  Purchase #2 $249.70   10.814%   $276.7026   $276.70   $276.70   $276.70  
  Purchase #3 $124.83   7.819%   $134.5905   $134.59   $134.60   $134.60  
  Purchase #4 $83.32   8.842%   $90.6872   $90.69   $90.70   $90.70  
  Purchase #5 $162.37   5.792%   $171.7745   $171.77   $171.75   $171.80  
  Purchase #6 $46.58   12.622%   $52.4593   $52.46   $52.45   $52.50  
  Purchase #7 $220.72   10.852%   $244.6725   $244.67   $244.65   $244.70  
  7 purchase totals = $901.29       $985.7914   $985.78   $985.75   $985.90