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 $59.36   6.548%   $63.2469   $63.25   $63.25   $63.20  
  Purchase #2 $35.53   6.752%   $37.929   $37.93   $37.95   $37.90  
  Purchase #3 $214.96   7.253%   $230.551   $230.55   $230.55   $230.60  
  Purchase #4 $238.94   10.865%   $264.9008   $264.90   $264.90   $264.90  
  Purchase #5 $79.65   8.331%   $86.2856   $86.29   $86.30   $86.30  
  Purchase #6 $108.46   9.639%   $118.9145   $118.91   $118.90   $118.90  
  Purchase #7 $179.75   5.627%   $189.8645   $189.86   $189.85   $189.90  
  7 purchase totals = $916.65       $991.6923   $991.69   $991.70   $991.70