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 $23.53   11.518%   $26.2402   $26.24   $26.25   $26.20  
  Purchase #2 $19.36   6.745%   $20.6658   $20.67   $20.65   $20.70  
  Purchase #3 $116.28   11.871%   $130.0836   $130.08   $130.10   $130.10  
  Purchase #4 $19.79   13.174%   $22.3971   $22.40   $22.40   $22.40  
  Purchase #5 $225.65   8.179%   $244.1059   $244.11   $244.10   $244.10  
  Purchase #6 $76.81   11.315%   $85.5011   $85.50   $85.50   $85.50  
  Purchase #7 $204.67   11.125%   $227.4395   $227.44   $227.45   $227.40  
  7 purchase totals = $686.09       $756.4332   $756.44   $756.45   $756.40