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 $202.57   3.139%   $208.9287   $208.93   $208.95   $208.90  
  Purchase #2 $94.31   6.196%   $100.1534   $100.15   $100.15   $100.20  
  Purchase #3 $110.38   7.725%   $118.9069   $118.91   $118.90   $118.90  
  Purchase #4 $153.36   6.655%   $163.5661   $163.57   $163.55   $163.60  
  Purchase #5 $245.48   7.625%   $264.1979   $264.20   $264.20   $264.20  
  Purchase #6 $52.96   8.188%   $57.2964   $57.30   $57.30   $57.30  
  Purchase #7 $88.45   10.230%   $97.4984   $97.50   $97.50   $97.50  
  7 purchase totals = $947.51       $1,010.5478   $1,010.56   $1,010.55   $1,010.60