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 $62.88   6.204%   $66.7811   $66.78   $66.80   $66.80  
  Purchase #2 $208.32   8.853%   $226.7626   $226.76   $226.75   $226.80  
  Purchase #3 $233.79   7.748%   $251.904   $251.90   $251.90   $251.90  
  Purchase #4 $65.87   4.385%   $68.7584   $68.76   $68.75   $68.80  
  Purchase #5 $227.76   9.281%   $248.8984   $248.90   $248.90   $248.90  
  Purchase #6 $151.68   13.281%   $171.8246   $171.82   $171.80   $171.80  
  Purchase #7 $117.55   6.830%   $125.5787   $125.58   $125.60   $125.60  
  7 purchase totals = $1,067.85       $1,160.5078   $1,160.50   $1,160.50   $1,160.60