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 $222.55   8.580%   $241.6448   $241.64   $241.65   $241.60  
  Purchase #2 $205.53   9.697%   $225.4602   $225.46   $225.45   $225.50  
  Purchase #3 $38.25   9.603%   $41.9231   $41.92   $41.90   $41.90  
  Purchase #4 $73.76   8.673%   $80.1572   $80.16   $80.15   $80.20  
  Purchase #5 $34.29   6.318%   $36.4564   $36.46   $36.45   $36.50  
  Purchase #6 $249.51   6.731%   $266.3045   $266.30   $266.30   $266.30  
  Purchase #7 $203.73   13.541%   $231.3171   $231.32   $231.30   $231.30  
  7 purchase totals = $1,027.62       $1,123.2633   $1,123.26   $1,123.20   $1,123.30