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 $207.89   3.323%   $214.7982   $214.80   $214.80   $214.80  
  Purchase #2 $237.75   12.244%   $266.8601   $266.86   $266.85   $266.90  
  Purchase #3 $39.99   13.567%   $45.4154   $45.42   $45.40   $45.40  
  Purchase #4 $15.60   3.252%   $16.1073   $16.11   $16.10   $16.10  
  Purchase #5 $175.93   12.720%   $198.3083   $198.31   $198.30   $198.30  
  Purchase #6 $89.68   7.513%   $96.4177   $96.42   $96.40   $96.40  
  Purchase #7 $147.51   13.313%   $167.148   $167.15   $167.15   $167.10  
  7 purchase totals = $914.35       $1,005.0550   $1,005.07   $1,005.00   $1,005.00