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 $248.74   8.485%   $269.8456   $269.85   $269.85   $269.80  
  Purchase #2 $121.36   4.351%   $126.6404   $126.64   $126.65   $126.60  
  Purchase #3 $70.44   11.546%   $78.573   $78.57   $78.55   $78.60  
  Purchase #4 $232.72   5.685%   $245.9501   $245.95   $245.95   $246.00  
  Purchase #5 $53.28   12.838%   $60.1201   $60.12   $60.10   $60.10  
  Purchase #6 $177.52   3.135%   $183.0853   $183.09   $183.10   $183.10  
  Purchase #7 $218.72   10.421%   $241.5128   $241.51   $241.50   $241.50  
  7 purchase totals = $1,122.78       $1,205.7273   $1,205.73   $1,205.70   $1,205.70