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	$156.35	11.411%	$174.1911	$174.19	$174.20	$174.20
Purchase #2	$76.66	9.174%	$83.6928	$83.69	$83.70	$83.70
Purchase #3	$75.33	9.659%	$82.6061	$82.61	$82.60	$82.60
Purchase #4	$153.34	6.242%	$162.9115	$162.91	$162.90	$162.90
Purchase #5	$59.81	13.311%	$67.7713	$67.77	$67.75	$67.80
Purchase #6	$225.70	6.658%	$240.7271	$240.73	$240.75	$240.70
Purchase #7	$36.88	10.652%	$40.8085	$40.81	$40.80	$40.80
7 purchase totals =	$784.07		$852.7084	$852.71	$852.70	$852.70