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 $101.40   13.205%   $114.7899   $114.79   $114.80   $114.80  
  Purchase #2 $162.77   8.440%   $176.5078   $176.51   $176.50   $176.50  
  Purchase #3 $37.45   9.771%   $41.1092   $41.11   $41.10   $41.10  
  Purchase #4 $19.26   12.867%   $21.7382   $21.74   $21.75   $21.70  
  Purchase #5 $246.65   10.422%   $272.3559   $272.36   $272.35   $272.40  
  Purchase #6 $180.60   11.866%   $202.03   $202.03   $202.05   $202.00  
  Purchase #7 $155.99   12.131%   $174.9131   $174.91   $174.90   $174.90  
  7 purchase totals = $904.12       $1,003.4441   $1,003.45   $1,003.45   $1,003.40