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 $65.95   11.813%   $73.7407   $73.74   $73.75   $73.70  
  Purchase #2 $53.27   6.689%   $56.8332   $56.83   $56.85   $56.80  
  Purchase #3 $7.84   12.434%   $8.8148   $8.81   $8.80   $8.80  
  Purchase #4 $69.67   5.308%   $73.3681   $73.37   $73.35   $73.40  
  Purchase #5 $163.82   12.715%   $184.6497   $184.65   $184.65   $184.60  
  Purchase #6 $76.97   8.454%   $83.477   $83.48   $83.50   $83.50  
  Purchase #7 $75.60   13.798%   $86.0313   $86.03   $86.05   $86.00  
  7 purchase totals = $513.12       $566.9148   $566.91   $566.95   $566.80