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 $23.56   13.392%   $26.7152   $26.72   $26.70   $26.70  
  Purchase #2 $122.67   6.508%   $130.6534   $130.65   $130.65   $130.70  
  Purchase #3 $56.55   9.633%   $61.9975   $62.00   $62.00   $62.00  
  Purchase #4 $105.62   6.585%   $112.5751   $112.58   $112.60   $112.60  
  Purchase #5 $22.81   6.869%   $24.3768   $24.38   $24.40   $24.40  
  Purchase #6 $35.86   3.215%   $37.0129   $37.01   $37.00   $37.00  
  Purchase #7 $182.54   13.293%   $206.805   $206.81   $206.80   $206.80  
  7 purchase totals = $549.61       $600.1359   $600.15   $600.15   $600.20