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 $247.61   8.452%   $268.538   $268.54   $268.55   $268.50  
  Purchase #2 $154.61   13.260%   $175.1113   $175.11   $175.10   $175.10  
  Purchase #3 $85.65   8.576%   $92.9953   $93.00   $93.00   $93.00  
  Purchase #4 $238.75   8.677%   $259.4663   $259.47   $259.45   $259.50  
  Purchase #5 $211.46   4.743%   $221.4895   $221.49   $221.50   $221.50  
  Purchase #6 $141.66   13.166%   $160.311   $160.31   $160.30   $160.30  
  Purchase #7 $34.72   8.862%   $37.7969   $37.80   $37.80   $37.80  
  7 purchase totals = $1,114.46       $1,215.7083   $1,215.72   $1,215.70   $1,215.70