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 $233.99   5.399%   $246.6231   $246.62   $246.60   $246.60  
  Purchase #2 $54.67   13.651%   $62.133   $62.13   $62.15   $62.10  
  Purchase #3 $221.59   9.240%   $242.0649   $242.06   $242.05   $242.10  
  Purchase #4 $144.67   13.564%   $164.293   $164.29   $164.30   $164.30  
  Purchase #5 $67.77   8.747%   $73.6978   $73.70   $73.70   $73.70  
  Purchase #6 $12.99   4.451%   $13.5682   $13.57   $13.55   $13.60  
  Purchase #7 $223.89   5.193%   $235.5166   $235.52   $235.50   $235.50  
  7 purchase totals = $959.57       $1,037.8966   $1,037.89   $1,037.85   $1,037.90