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 $239.50   10.356%   $264.3026   $264.30   $264.30   $264.30  
  Purchase #2 $164.61   10.791%   $182.3731   $182.37   $182.35   $182.40  
  Purchase #3 $226.52   11.182%   $251.8495   $251.85   $251.85   $251.80  
  Purchase #4 $169.84   4.856%   $178.0874   $178.09   $178.10   $178.10  
  Purchase #5 $95.77   3.862%   $99.4686   $99.47   $99.45   $99.50  
  Purchase #6 $160.42   4.327%   $167.3614   $167.36   $167.35   $167.40  
  Purchase #7 $203.47   8.366%   $220.4923   $220.49   $220.50   $220.50  
  7 purchase totals = $1,260.13       $1,363.9349   $1,363.93   $1,363.90   $1,364.00