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 $98.65   6.169%   $104.7357   $104.74   $104.75   $104.70  
  Purchase #2 $248.35   4.309%   $259.0514   $259.05   $259.05   $259.10  
  Purchase #3 $71.69   11.574%   $79.9874   $79.99   $80.00   $80.00  
  Purchase #4 $5.36   11.158%   $5.9581   $5.96   $5.95   $6.00  
  Purchase #5 $53.68   4.873%   $56.2958   $56.30   $56.30   $56.30  
  Purchase #6 $249.29   4.425%   $260.3211   $260.32   $260.30   $260.30  
  Purchase #7 $85.43   10.762%   $94.624   $94.62   $94.60   $94.60  
  7 purchase totals = $812.45       $860.9735   $860.98   $860.95   $861.00