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 $66.72   3.426%   $69.0058   $69.01   $69.00   $69.00  
  Purchase #2 $185.80   10.707%   $205.6936   $205.69   $205.70   $205.70  
  Purchase #3 $240.65   6.405%   $256.0636   $256.06   $256.05   $256.10  
  Purchase #4 $92.89   7.524%   $99.879   $99.88   $99.90   $99.90  
  Purchase #5 $17.27   8.245%   $18.6939   $18.69   $18.70   $18.70  
  Purchase #6 $167.58   6.286%   $178.1141   $178.11   $178.10   $178.10  
  Purchase #7 $113.81   9.528%   $124.6538   $124.65   $124.65   $124.70  
  7 purchase totals = $884.72       $952.1038   $952.09   $952.10   $952.20