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 $43.48   8.245%   $47.0649   $47.06   $47.05   $47.10  
  Purchase #2 $190.80   11.656%   $213.0396   $213.04   $213.05   $213.00  
  Purchase #3 $223.70   13.788%   $254.5438   $254.54   $254.55   $254.50  
  Purchase #4 $12.87   5.409%   $13.5661   $13.57   $13.55   $13.60  
  Purchase #5 $77.83   9.666%   $85.353   $85.35   $85.35   $85.40  
  Purchase #6 $62.34   12.591%   $70.1892   $70.19   $70.20   $70.20  
  Purchase #7 $223.66   11.437%   $249.24   $249.24   $249.25   $249.20  
  7 purchase totals = $834.68       $932.9966   $932.99   $933.00   $933.00