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 $202.32   11.834%   $226.2625   $226.26   $226.25   $226.30  
  Purchase #2 $222.59   6.391%   $236.8157   $236.82   $236.80   $236.80  
  Purchase #3 $206.48   6.298%   $219.4841   $219.48   $219.50   $219.50  
  Purchase #4 $246.38   3.120%   $254.0671   $254.07   $254.05   $254.10  
  Purchase #5 $224.77   13.841%   $255.8804   $255.88   $255.90   $255.90  
  Purchase #6 $142.92   12.237%   $160.4091   $160.41   $160.40   $160.40  
  Purchase #7 $192.38   10.363%   $212.3163   $212.32   $212.30   $212.30  
  7 purchase totals = $1,437.84       $1,565.2352   $1,565.24   $1,565.20   $1,565.30