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 $227.81   11.616%   $254.2724   $254.27   $254.25   $254.30  
  Purchase #2 $76.87   13.318%   $87.1075   $87.11   $87.10   $87.10  
  Purchase #3 $62.89   3.408%   $65.0333   $65.03   $65.05   $65.00  
  Purchase #4 $53.77   7.761%   $57.9431   $57.94   $57.95   $57.90  
  Purchase #5 $165.77   9.207%   $181.0324   $181.03   $181.05   $181.00  
  Purchase #6 $121.46   7.254%   $130.2707   $130.27   $130.25   $130.30  
  Purchase #7 $48.36   6.515%   $51.5107   $51.51   $51.50   $51.50  
  7 purchase totals = $756.93       $827.1701   $827.16   $827.15   $827.10