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 $42.70   11.478%   $47.6011   $47.60   $47.60   $47.60  
  Purchase #2 $141.75   3.567%   $146.8062   $146.81   $146.80   $146.80  
  Purchase #3 $226.99   6.526%   $241.8034   $241.80   $241.80   $241.80  
  Purchase #4 $169.60   4.140%   $176.6214   $176.62   $176.60   $176.60  
  Purchase #5 $117.40   11.497%   $130.8975   $130.90   $130.90   $130.90  
  Purchase #6 $24.63   9.474%   $26.9634   $26.96   $26.95   $27.00  
  Purchase #7 $228.35   11.806%   $255.309   $255.31   $255.30   $255.30  
  7 purchase totals = $951.42       $1,026.0020   $1,026.00   $1,025.95   $1,026.00