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 $115.68   13.736%   $131.5698   $131.57   $131.55   $131.60  
  Purchase #2 $184.96   11.368%   $205.9863   $205.99   $206.00   $206.00  
  Purchase #3 $180.54   10.519%   $199.531   $199.53   $199.55   $199.50  
  Purchase #4 $106.86   11.730%   $119.3947   $119.39   $119.40   $119.40  
  Purchase #5 $219.93   12.122%   $246.5899   $246.59   $246.60   $246.60  
  Purchase #6 $182.51   7.549%   $196.2877   $196.29   $196.30   $196.30  
  Purchase #7 $48.75   13.409%   $55.2869   $55.29   $55.30   $55.30  
  7 purchase totals = $1,039.23       $1,154.6463   $1,154.65   $1,154.70   $1,154.70