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 $119.30   12.846%   $134.6253   $134.63   $134.65   $134.60  
  Purchase #2 $45.78   8.526%   $49.6832   $49.68   $49.70   $49.70  
  Purchase #3 $117.67   8.187%   $127.3036   $127.30   $127.30   $127.30  
  Purchase #4 $114.54   10.162%   $126.1796   $126.18   $126.20   $126.20  
  Purchase #5 $122.30   12.346%   $137.3992   $137.40   $137.40   $137.40  
  Purchase #6 $175.42   6.476%   $186.7802   $186.78   $186.80   $186.80  
  Purchase #7 $206.30   8.378%   $223.5838   $223.58   $223.60   $223.60  
  7 purchase totals = $901.31       $985.5549   $985.55   $985.65   $985.60