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	$215.28	11.138%	$239.2579	$239.26	$239.25	$239.30
Purchase #2	$61.57	5.299%	$64.8326	$64.83	$64.85	$64.80
Purchase #3	$73.56	6.426%	$78.287	$78.29	$78.30	$78.30
Purchase #4	$226.43	10.819%	$250.9275	$250.93	$250.95	$250.90
Purchase #5	$90.56	12.534%	$101.9108	$101.91	$101.90	$101.90
Purchase #6	$248.48	11.199%	$276.3073	$276.31	$276.30	$276.30
Purchase #7	$136.86	8.336%	$148.2686	$148.27	$148.25	$148.30
7 purchase totals =	$1,052.74		$1,159.7917	$1,159.80	$1,159.80	$1,159.80