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	$194.25	7.467%	$208.7546	$208.75	$208.75	$208.80
Purchase #2	$243.78	12.287%	$273.7332	$273.73	$273.75	$273.70
Purchase #3	$227.86	5.510%	$240.4151	$240.42	$240.40	$240.40
Purchase #4	$43.48	4.801%	$45.5675	$45.57	$45.55	$45.60
Purchase #5	$172.48	9.755%	$189.3054	$189.31	$189.30	$189.30
Purchase #6	$171.77	12.241%	$192.7964	$192.80	$192.80	$192.80
Purchase #7	$57.74	8.623%	$62.7189	$62.72	$62.70	$62.70
7 purchase totals =	$1,111.36		$1,213.2911	$1,213.30	$1,213.25	$1,213.30