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	$28.37	13.430%	$32.1801	$32.18	$32.20	$32.20
Purchase #2	$105.96	8.412%	$114.8734	$114.87	$114.85	$114.90
Purchase #3	$59.89	5.601%	$63.2444	$63.24	$63.25	$63.20
Purchase #4	$128.39	9.289%	$140.3161	$140.32	$140.30	$140.30
Purchase #5	$238.32	5.701%	$251.9066	$251.91	$251.90	$251.90
Purchase #6	$243.89	10.119%	$268.5692	$268.57	$268.55	$268.60
Purchase #7	$248.71	4.562%	$260.0562	$260.06	$260.05	$260.10
7 purchase totals =	$1,053.53		$1,131.1460	$1,131.15	$1,131.10	$1,131.20