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 $52.67   12.156%   $59.0726   $59.07   $59.05   $59.10  
  Purchase #2 $18.26   5.861%   $19.3302   $19.33   $19.35   $19.30  
  Purchase #3 $99.69   5.462%   $105.1351   $105.14   $105.15   $105.10  
  Purchase #4 $121.36   8.819%   $132.0627   $132.06   $132.05   $132.10  
  Purchase #5 $116.35   12.693%   $131.1183   $131.12   $131.10   $131.10  
  Purchase #6 $187.93   5.259%   $197.8132   $197.81   $197.80   $197.80  
  Purchase #7 $74.86   8.298%   $81.0719   $81.07   $81.05   $81.10  
  7 purchase totals = $671.12       $725.6040   $725.60   $725.55   $725.60