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 $55.91   12.688%   $63.0039   $63.00   $63.00   $63.00  
  Purchase #2 $68.85   7.158%   $73.7783   $73.78   $73.80   $73.80  
  Purchase #3 $246.26   7.691%   $265.1999   $265.20   $265.20   $265.20  
  Purchase #4 $114.62   5.298%   $120.6926   $120.69   $120.70   $120.70  
  Purchase #5 $231.26   11.638%   $258.174   $258.17   $258.15   $258.20  
  Purchase #6 $146.40   7.263%   $157.033   $157.03   $157.05   $157.00  
  Purchase #7 $113.64   7.370%   $122.0153   $122.02   $122.00   $122.00  
  7 purchase totals = $976.94       $1,059.8970   $1,059.89   $1,059.90   $1,059.90