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 $245.36   7.705%   $264.265   $264.27   $264.25   $264.30  
  Purchase #2 $167.26   4.711%   $175.1396   $175.14   $175.15   $175.10  
  Purchase #3 $16.44   9.705%   $18.0355   $18.04   $18.05   $18.00  
  Purchase #4 $71.87   3.437%   $74.3402   $74.34   $74.35   $74.30  
  Purchase #5 $175.76   5.155%   $184.8204   $184.82   $184.80   $184.80  
  Purchase #6 $46.74   10.508%   $51.6514   $51.65   $51.65   $51.70  
  Purchase #7 $34.48   9.224%   $37.6604   $37.66   $37.65   $37.70  
  7 purchase totals = $757.91       $805.9125   $805.92   $805.90   $805.90