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 $247.41   11.440%   $275.7137   $275.71   $275.70   $275.70  
  Purchase #2 $44.27   11.872%   $49.5257   $49.53   $49.55   $49.50  
  Purchase #3 $15.97   10.173%   $17.5946   $17.59   $17.60   $17.60  
  Purchase #4 $137.65   5.833%   $145.6791   $145.68   $145.70   $145.70  
  Purchase #5 $119.51   6.796%   $127.6319   $127.63   $127.65   $127.60  
  Purchase #6 $166.71   3.418%   $172.4081   $172.41   $172.40   $172.40  
  Purchase #7 $169.85   4.811%   $178.0215   $178.02   $178.00   $178.00  
  7 purchase totals = $901.37       $966.5746   $966.57   $966.60   $966.50