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 $222.79   10.474%   $246.125   $246.13   $246.15   $246.10  
  Purchase #2 $141.72   4.710%   $148.395   $148.40   $148.40   $148.40  
  Purchase #3 $138.43   12.654%   $155.9469   $155.95   $155.95   $155.90  
  Purchase #4 $157.48   4.866%   $165.143   $165.14   $165.15   $165.10  
  Purchase #5 $61.65   6.524%   $65.672   $65.67   $65.65   $65.70  
  Purchase #6 $229.76   7.860%   $247.8191   $247.82   $247.80   $247.80  
  Purchase #7 $42.54   9.574%   $46.6128   $46.61   $46.60   $46.60  
  7 purchase totals = $994.37       $1,075.7138   $1,075.72   $1,075.70   $1,075.60