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 $29.69   9.738%   $32.5812   $32.58   $32.60   $32.60  
  Purchase #2 $86.91   12.112%   $97.4365   $97.44   $97.45   $97.40  
  Purchase #3 $122.83   7.588%   $132.1503   $132.15   $132.15   $132.20  
  Purchase #4 $153.76   12.218%   $172.5464   $172.55   $172.55   $172.50  
  Purchase #5 $69.49   3.143%   $71.6741   $71.67   $71.65   $71.70  
  Purchase #6 $191.26   9.631%   $209.6803   $209.68   $209.70   $209.70  
  Purchase #7 $235.75   4.663%   $246.743   $246.74   $246.75   $246.70  
  7 purchase totals = $889.69       $962.8118   $962.81   $962.85   $962.80