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 $163.61   8.253%   $177.1127   $177.11   $177.10   $177.10  
  Purchase #2 $211.97   10.866%   $235.0027   $235.00   $235.00   $235.00  
  Purchase #3 $170.33   10.268%   $187.8195   $187.82   $187.80   $187.80  
  Purchase #4 $114.39   11.867%   $127.9647   $127.96   $127.95   $128.00  
  Purchase #5 $105.30   6.430%   $112.0708   $112.07   $112.05   $112.10  
  Purchase #6 $27.60   5.662%   $29.1627   $29.16   $29.15   $29.20  
  Purchase #7 $160.34   7.425%   $172.2452   $172.25   $172.25   $172.20  
  7 purchase totals = $953.54       $1,041.3783   $1,041.37   $1,041.30   $1,041.40