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 $184.68   13.303%   $209.248   $209.25   $209.25   $209.20  
  Purchase #2 $163.54   10.304%   $180.3912   $180.39   $180.40   $180.40  
  Purchase #3 $24.92   7.122%   $26.6948   $26.69   $26.70   $26.70  
  Purchase #4 $105.82   13.256%   $119.8475   $119.85   $119.85   $119.80  
  Purchase #5 $58.76   10.784%   $65.0967   $65.10   $65.10   $65.10  
  Purchase #6 $168.51   13.565%   $191.3684   $191.37   $191.35   $191.40  
  Purchase #7 $73.52   10.248%   $81.0543   $81.05   $81.05   $81.10  
  7 purchase totals = $779.75       $873.7009   $873.70   $873.70   $873.70