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 $87.74   9.855%   $96.3868   $96.39   $96.40   $96.40  
  Purchase #2 $119.25   12.595%   $134.2695   $134.27   $134.25   $134.30  
  Purchase #3 $124.33   6.111%   $131.9278   $131.93   $131.95   $131.90  
  Purchase #4 $237.54   13.216%   $268.9333   $268.93   $268.95   $268.90  
  Purchase #5 $154.34   9.752%   $169.3912   $169.39   $169.40   $169.40  
  Purchase #6 $52.91   9.454%   $57.9121   $57.91   $57.90   $57.90  
  Purchase #7 $198.95   6.831%   $212.5403   $212.54   $212.55   $212.50  
  7 purchase totals = $975.06       $1,071.3610   $1,071.36   $1,071.40   $1,071.30