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 $208.33   8.856%   $226.7797   $226.78   $226.80   $226.80  
  Purchase #2 $74.95   13.861%   $85.3388   $85.34   $85.35   $85.30  
  Purchase #3 $150.37   10.865%   $166.7077   $166.71   $166.70   $166.70  
  Purchase #4 $233.69   9.444%   $255.7597   $255.76   $255.75   $255.80  
  Purchase #5 $77.41   6.624%   $82.5376   $82.54   $82.55   $82.50  
  Purchase #6 $53.96   11.735%   $60.2922   $60.29   $60.30   $60.30  
  Purchase #7 $116.93   3.428%   $120.9384   $120.94   $120.95   $120.90  
  7 purchase totals = $915.64       $998.3541   $998.36   $998.40   $998.30