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 $26.88   10.293%   $29.6468   $29.65   $29.65   $29.60  
  Purchase #2 $154.84   7.591%   $166.5939   $166.59   $166.60   $166.60  
  Purchase #3 $33.64   5.668%   $35.5467   $35.55   $35.55   $35.50  
  Purchase #4 $42.78   6.115%   $45.396   $45.40   $45.40   $45.40  
  Purchase #5 $192.72   5.556%   $203.4275   $203.43   $203.45   $203.40  
  Purchase #6 $152.50   3.578%   $157.9565   $157.96   $157.95   $158.00  
  Purchase #7 $249.83   8.116%   $270.1062   $270.11   $270.10   $270.10  
  7 purchase totals = $853.19       $908.6736   $908.69   $908.70   $908.60