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 $58.92   10.319%   $65   $65.00   $65.00   $65.00  
  Purchase #2 $67.50   4.791%   $70.7339   $70.73   $70.75   $70.70  
  Purchase #3 $49.85   11.147%   $55.4068   $55.41   $55.40   $55.40  
  Purchase #4 $66.89   8.355%   $72.4787   $72.48   $72.50   $72.50  
  Purchase #5 $80.45   4.210%   $83.8369   $83.84   $83.85   $83.80  
  Purchase #6 $208.84   8.540%   $226.6749   $226.67   $226.65   $226.70  
  Purchase #7 $243.64   3.774%   $252.835   $252.84   $252.85   $252.80  
  7 purchase totals = $776.09       $826.9662   $826.97   $827.00   $826.90