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 $94.86   12.368%   $106.5923   $106.59   $106.60   $106.60  
  Purchase #2 $205.58   3.202%   $212.1627   $212.16   $212.15   $212.20  
  Purchase #3 $56.40   5.642%   $59.5821   $59.58   $59.60   $59.60  
  Purchase #4 $238.36   4.393%   $248.8312   $248.83   $248.85   $248.80  
  Purchase #5 $90.80   13.608%   $103.1561   $103.16   $103.15   $103.20  
  Purchase #6 $5.41   7.192%   $5.7991   $5.80   $5.80   $5.80  
  Purchase #7 $162.69   11.549%   $181.4791   $181.48   $181.50   $181.50  
  7 purchase totals = $854.10       $917.6026   $917.60   $917.65   $917.70