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	$50.53	11.279%	$56.2293	$56.23	$56.25	$56.20
Purchase #2	$79.63	12.675%	$89.7231	$89.72	$89.70	$89.70
Purchase #3	$211.66	13.801%	$240.8712	$240.87	$240.85	$240.90
Purchase #4	$61.96	10.475%	$68.4503	$68.45	$68.45	$68.50
Purchase #5	$25.95	11.424%	$28.9145	$28.91	$28.90	$28.90
Purchase #6	$230.61	13.308%	$261.2996	$261.30	$261.30	$261.30
Purchase #7	$245.43	9.147%	$267.8795	$267.88	$267.90	$267.90
7 purchase totals =	$905.77		$1,013.3675	$1,013.36	$1,013.35	$1,013.40