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 $112.77   12.407%   $126.7614   $126.76   $126.75   $126.80  
  Purchase #2 $223.54   4.243%   $233.0248   $233.02   $233.00   $233.00  
  Purchase #3 $61.54   12.247%   $69.0768   $69.08   $69.10   $69.10  
  Purchase #4 $41.93   12.843%   $47.3151   $47.32   $47.30   $47.30  
  Purchase #5 $235.59   11.429%   $262.5156   $262.52   $262.50   $262.50  
  Purchase #6 $230.92   6.315%   $245.5026   $245.50   $245.50   $245.50  
  Purchase #7 $82.38   12.474%   $92.6561   $92.66   $92.65   $92.70  
  7 purchase totals = $988.67       $1,076.8524   $1,076.86   $1,076.80   $1,076.90