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 $250.66   10.248%   $276.3476   $276.35   $276.35   $276.30  
  Purchase #2 $136.62   9.334%   $149.3721   $149.37   $149.35   $149.40  
  Purchase #3 $244.71   9.717%   $268.4885   $268.49   $268.50   $268.50  
  Purchase #4 $59.68   6.449%   $63.5288   $63.53   $63.55   $63.50  
  Purchase #5 $33.33   11.385%   $37.1246   $37.12   $37.10   $37.10  
  Purchase #6 $196.89   4.703%   $206.1497   $206.15   $206.15   $206.10  
  Purchase #7 $154.76   13.334%   $175.3957   $175.40   $175.40   $175.40  
  7 purchase totals = $1,076.65       $1,176.4070   $1,176.41   $1,176.40   $1,176.30