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 $135.46   5.701%   $143.1826   $143.18   $143.20   $143.20  
  Purchase #2 $176.79   11.318%   $196.7991   $196.80   $196.80   $196.80  
  Purchase #3 $183.85   8.866%   $200.1501   $200.15   $200.15   $200.20  
  Purchase #4 $76.90   7.332%   $82.5383   $82.54   $82.55   $82.50  
  Purchase #5 $198.58   6.708%   $211.9007   $211.90   $211.90   $211.90  
  Purchase #6 $118.29   13.642%   $134.4271   $134.43   $134.45   $134.40  
  Purchase #7 $47.87   8.557%   $51.9662   $51.97   $51.95   $52.00  
  7 purchase totals = $937.74       $1,020.9641   $1,020.97   $1,021.00   $1,021.00