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 $185.59   12.613%   $208.9985   $209.00   $209.00   $209.00  
  Purchase #2 $225.95   3.109%   $232.9748   $232.97   $232.95   $233.00  
  Purchase #3 $221.58   6.778%   $236.5987   $236.60   $236.60   $236.60  
  Purchase #4 $149.82   8.307%   $162.2655   $162.27   $162.25   $162.30  
  Purchase #5 $77.85   11.525%   $86.8222   $86.82   $86.80   $86.80  
  Purchase #6 $57.53   13.498%   $65.2954   $65.30   $65.30   $65.30  
  Purchase #7 $230.28   3.603%   $238.577   $238.58   $238.60   $238.60  
  7 purchase totals = $1,148.60       $1,231.5321   $1,231.54   $1,231.50   $1,231.60