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 $50.83   6.136%   $53.9489   $53.95   $53.95   $53.90  
  Purchase #2 $59.97   6.235%   $63.7091   $63.71   $63.70   $63.70  
  Purchase #3 $183.77   8.140%   $198.7289   $198.73   $198.75   $198.70  
  Purchase #4 $90.32   6.239%   $95.9551   $95.96   $95.95   $96.00  
  Purchase #5 $240.56   9.388%   $263.1438   $263.14   $263.15   $263.10  
  Purchase #6 $72.81   7.538%   $78.2984   $78.30   $78.30   $78.30  
  Purchase #7 $177.29   4.203%   $184.7415   $184.74   $184.75   $184.70  
  7 purchase totals = $875.55       $938.5257   $938.53   $938.55   $938.40