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 $56.99   13.178%   $64.5001   $64.50   $64.50   $64.50  
  Purchase #2 $221.76   6.722%   $236.6667   $236.67   $236.65   $236.70  
  Purchase #3 $184.38   10.801%   $204.2949   $204.29   $204.30   $204.30  
  Purchase #4 $166.89   3.191%   $172.2155   $172.22   $172.20   $172.20  
  Purchase #5 $155.29   13.833%   $176.7713   $176.77   $176.75   $176.80  
  Purchase #6 $231.80   13.564%   $263.2414   $263.24   $263.25   $263.20  
  Purchase #7 $165.50   9.295%   $180.8832   $180.88   $180.90   $180.90  
  7 purchase totals = $1,182.61       $1,298.5731   $1,298.57   $1,298.55   $1,298.60