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 $89.87   3.859%   $93.3381   $93.34   $93.35   $93.30  
  Purchase #2 $31.71   11.243%   $35.2752   $35.28   $35.30   $35.30  
  Purchase #3 $230.66   7.686%   $248.3885   $248.39   $248.40   $248.40  
  Purchase #4 $181.37   8.283%   $196.3929   $196.39   $196.40   $196.40  
  Purchase #5 $152.98   5.802%   $161.8559   $161.86   $161.85   $161.90  
  Purchase #6 $23.48   10.777%   $26.0104   $26.01   $26.00   $26.00  
  Purchase #7 $200.59   11.191%   $223.038   $223.04   $223.05   $223.00  
  7 purchase totals = $910.66       $984.2990   $984.31   $984.35   $984.30