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	$132.63	4.617%	$138.7535	$138.75	$138.75	$138.80
Purchase #2	$54.78	9.200%	$59.8198	$59.82	$59.80	$59.80
Purchase #3	$37.83	11.544%	$42.1971	$42.20	$42.20	$42.20
Purchase #4	$65.41	11.774%	$73.1114	$73.11	$73.10	$73.10
Purchase #5	$191.40	4.648%	$200.2963	$200.30	$200.30	$200.30
Purchase #6	$76.73	11.472%	$85.5325	$85.53	$85.55	$85.50
Purchase #7	$208.46	4.627%	$218.1054	$218.11	$218.10	$218.10
7 purchase totals =	$767.24		$817.8160	$817.82	$817.80	$817.80