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	$250.63	5.788%	$265.1365	$265.14	$265.15	$265.10
Purchase #2	$113.40	8.742%	$123.3134	$123.31	$123.30	$123.30
Purchase #3	$84.92	5.228%	$89.3596	$89.36	$89.35	$89.40
Purchase #4	$189.82	11.453%	$211.5601	$211.56	$211.55	$211.60
Purchase #5	$197.80	7.813%	$213.2541	$213.25	$213.25	$213.30
Purchase #6	$89.29	3.793%	$92.6768	$92.68	$92.70	$92.70
Purchase #7	$211.48	13.745%	$240.5479	$240.55	$240.55	$240.50
7 purchase totals =	$1,137.34		$1,235.8484	$1,235.85	$1,235.85	$1,235.90