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 $238.26   12.442%   $267.9043   $267.90   $267.90   $267.90  
  Purchase #2 $113.94   3.264%   $117.659   $117.66   $117.65   $117.70  
  Purchase #3 $48.49   13.870%   $55.2156   $55.22   $55.20   $55.20  
  Purchase #4 $113.71   12.106%   $127.4757   $127.48   $127.50   $127.50  
  Purchase #5 $203.76   12.572%   $229.3767   $229.38   $229.40   $229.40  
  Purchase #6 $34.33   12.705%   $38.6916   $38.69   $38.70   $38.70  
  Purchase #7 $212.66   6.559%   $226.6084   $226.61   $226.60   $226.60  
  7 purchase totals = $965.15       $1,062.9313   $1,062.94   $1,062.95   $1,063.00