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 $119.50   11.260%   $132.9557   $132.96   $132.95   $133.00  
  Purchase #2 $177.85   8.321%   $192.6489   $192.65   $192.65   $192.60  
  Purchase #3 $172.52   7.150%   $184.8552   $184.86   $184.85   $184.90  
  Purchase #4 $244.46   7.785%   $263.4912   $263.49   $263.50   $263.50  
  Purchase #5 $53.70   5.269%   $56.5295   $56.53   $56.55   $56.50  
  Purchase #6 $214.60   7.872%   $231.4933   $231.49   $231.50   $231.50  
  Purchase #7 $239.62   5.612%   $253.0675   $253.07   $253.05   $253.10  
  7 purchase totals = $1,222.25       $1,315.0413   $1,315.05   $1,315.05   $1,315.10