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	$50.48	3.627%	$52.3109	$52.31	$52.30	$52.30
Purchase #2	$241.90	12.489%	$272.1109	$272.11	$272.10	$272.10
Purchase #3	$85.58	7.399%	$91.9121	$91.91	$91.90	$91.90
Purchase #4	$85.71	12.351%	$96.296	$96.30	$96.30	$96.30
Purchase #5	$248.64	4.545%	$259.9407	$259.94	$259.95	$259.90
Purchase #6	$136.61	7.768%	$147.2219	$147.22	$147.20	$147.20
Purchase #7	$152.90	5.586%	$161.441	$161.44	$161.45	$161.40
7 purchase totals =	$1,001.82		$1,081.2335	$1,081.23	$1,081.20	$1,081.10