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 $84.93   9.374%   $92.8913   $92.89   $92.90   $92.90  
  Purchase #2 $218.46   9.705%   $239.6615   $239.66   $239.65   $239.70  
  Purchase #3 $15.29   12.691%   $17.2305   $17.23   $17.25   $17.20  
  Purchase #4 $17.44   11.408%   $19.4296   $19.43   $19.45   $19.40  
  Purchase #5 $59.83   9.139%   $65.2979   $65.30   $65.30   $65.30  
  Purchase #6 $17.49   4.356%   $18.2519   $18.25   $18.25   $18.30  
  Purchase #7 $207.91   9.714%   $228.1064   $228.11   $228.10   $228.10  
  7 purchase totals = $621.35       $680.8691   $680.87   $680.90   $680.90