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	$28.88	12.515%	$32.4943	$32.49	$32.50	$32.50
Purchase #2	$219.65	3.673%	$227.7177	$227.72	$227.70	$227.70
Purchase #3	$35.59	6.221%	$37.8041	$37.80	$37.80	$37.80
Purchase #4	$126.73	7.660%	$136.4375	$136.44	$136.45	$136.40
Purchase #5	$170.27	10.618%	$188.3493	$188.35	$188.35	$188.30
Purchase #6	$161.33	11.743%	$180.275	$180.28	$180.30	$180.30
Purchase #7	$198.69	5.240%	$209.1014	$209.10	$209.10	$209.10
7 purchase totals =	$941.14		$1,012.1793	$1,012.18	$1,012.20	$1,012.10