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 $82.73   3.319%   $85.4758   $85.48   $85.50   $85.50  
  Purchase #2 $120.71   3.329%   $124.7284   $124.73   $124.75   $124.70  
  Purchase #3 $142.28   13.482%   $161.4622   $161.46   $161.45   $161.50  
  Purchase #4 $218.91   6.661%   $233.4916   $233.49   $233.50   $233.50  
  Purchase #5 $8.64   5.304%   $9.0983   $9.10   $9.10   $9.10  
  Purchase #6 $159.37   12.709%   $179.6243   $179.62   $179.60   $179.60  
  Purchase #7 $103.58   13.381%   $117.44   $117.44   $117.45   $117.40  
  7 purchase totals = $836.22       $911.3206   $911.32   $911.35   $911.30