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 $29.88   9.147%   $32.6131   $32.61   $32.60   $32.60  
  Purchase #2 $57.39   7.324%   $61.5932   $61.59   $61.60   $61.60  
  Purchase #3 $93.83   9.415%   $102.6641   $102.66   $102.65   $102.70  
  Purchase #4 $163.70   4.854%   $171.646   $171.65   $171.65   $171.60  
  Purchase #5 $27.36   12.116%   $30.6749   $30.67   $30.65   $30.70  
  Purchase #6 $113.95   9.298%   $124.5451   $124.55   $124.55   $124.50  
  Purchase #7 $20.83   9.298%   $22.7668   $22.77   $22.75   $22.80  
  7 purchase totals = $506.94       $546.5032   $546.50   $546.45   $546.50