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 $247.29   5.866%   $261.796   $261.80   $261.80   $261.80  
  Purchase #2 $47.27   13.265%   $53.5404   $53.54   $53.55   $53.50  
  Purchase #3 $24.25   10.300%   $26.7478   $26.75   $26.75   $26.70  
  Purchase #4 $57.30   6.596%   $61.0795   $61.08   $61.10   $61.10  
  Purchase #5 $102.45   6.281%   $108.8849   $108.88   $108.90   $108.90  
  Purchase #6 $203.56   9.664%   $223.232   $223.23   $223.25   $223.20  
  Purchase #7 $173.61   4.703%   $181.7749   $181.77   $181.75   $181.80  
  7 purchase totals = $855.73       $917.0555   $917.05   $917.10   $917.00