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 $83.26   12.487%   $93.6567   $93.66   $93.65   $93.70  
  Purchase #2 $246.40   8.756%   $267.9748   $267.97   $267.95   $268.00  
  Purchase #3 $25.66   4.600%   $26.8404   $26.84   $26.85   $26.80  
  Purchase #4 $187.59   3.144%   $193.4878   $193.49   $193.50   $193.50  
  Purchase #5 $63.50   3.312%   $65.6031   $65.60   $65.60   $65.60  
  Purchase #6 $175.78   11.312%   $195.6642   $195.66   $195.65   $195.70  
  Purchase #7 $57.26   7.312%   $61.4469   $61.45   $61.45   $61.40  
  7 purchase totals = $839.45       $904.6739   $904.67   $904.65   $904.70