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 $171.99   3.653%   $178.2728   $178.27   $178.25   $178.30  
  Purchase #2 $14.44   10.232%   $15.9175   $15.92   $15.90   $15.90  
  Purchase #3 $87.39   10.488%   $96.5555   $96.56   $96.55   $96.60  
  Purchase #4 $233.75   6.199%   $248.2402   $248.24   $248.25   $248.20  
  Purchase #5 $202.64   6.378%   $215.5644   $215.56   $215.55   $215.60  
  Purchase #6 $189.89   11.762%   $212.2249   $212.22   $212.20   $212.20  
  Purchase #7 $67.29   4.563%   $70.3604   $70.36   $70.35   $70.40  
  7 purchase totals = $967.39       $1,037.1357   $1,037.13   $1,037.05   $1,037.20