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 $59.73   10.449%   $65.9712   $65.97   $65.95   $66.00  
  Purchase #2 $142.58   4.264%   $148.6596   $148.66   $148.65   $148.70  
  Purchase #3 $194.52   6.784%   $207.7162   $207.72   $207.70   $207.70  
  Purchase #4 $37.25   3.361%   $38.502   $38.50   $38.50   $38.50  
  Purchase #5 $158.33   8.228%   $171.3574   $171.36   $171.35   $171.40  
  Purchase #6 $22.45   4.677%   $23.5   $23.50   $23.50   $23.50  
  Purchase #7 $37.98   7.337%   $40.7666   $40.77   $40.75   $40.80  
  7 purchase totals = $652.84       $696.4730   $696.48   $696.40   $696.60