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 $228.98   10.645%   $253.3549   $253.35   $253.35   $253.40  
  Purchase #2 $58.87   12.724%   $66.3606   $66.36   $66.35   $66.40  
  Purchase #3 $15.38   10.277%   $16.9606   $16.96   $16.95   $17.00  
  Purchase #4 $197.66   4.349%   $206.2562   $206.26   $206.25   $206.30  
  Purchase #5 $47.93   8.416%   $51.9638   $51.96   $51.95   $52.00  
  Purchase #6 $158.46   10.422%   $174.9747   $174.97   $174.95   $175.00  
  Purchase #7 $240.81   6.111%   $255.5259   $255.53   $255.55   $255.50  
  7 purchase totals = $948.09       $1,025.3967   $1,025.39   $1,025.35   $1,025.60