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 $78.81   12.542%   $88.6944   $88.69   $88.70   $88.70  
  Purchase #2 $74.86   13.335%   $84.8426   $84.84   $84.85   $84.80  
  Purchase #3 $119.93   4.371%   $125.1721   $125.17   $125.15   $125.20  
  Purchase #4 $63.98   7.404%   $68.7171   $68.72   $68.70   $68.70  
  Purchase #5 $184.44   9.309%   $201.6095   $201.61   $201.60   $201.60  
  Purchase #6 $117.31   8.177%   $126.9024   $126.90   $126.90   $126.90  
  Purchase #7 $239.61   8.482%   $259.9337   $259.93   $259.95   $259.90  
  7 purchase totals = $878.94       $955.8718   $955.86   $955.85   $955.80