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 $87.76   9.759%   $96.3245   $96.32   $96.30   $96.30  
  Purchase #2 $65.46   9.291%   $71.5419   $71.54   $71.55   $71.50  
  Purchase #3 $117.90   4.369%   $123.0511   $123.05   $123.05   $123.10  
  Purchase #4 $126.67   13.349%   $143.5792   $143.58   $143.60   $143.60  
  Purchase #5 $231.51   9.244%   $252.9108   $252.91   $252.90   $252.90  
  Purchase #6 $20.33   12.252%   $22.8208   $22.82   $22.80   $22.80  
  Purchase #7 $245.45   3.690%   $254.5071   $254.51   $254.50   $254.50  
  7 purchase totals = $895.08       $964.7354   $964.73   $964.70   $964.70