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	$195.32	12.219%	$219.1862	$219.19	$219.20	$219.20
Purchase #2	$92.34	8.398%	$100.0947	$100.09	$100.10	$100.10
Purchase #3	$100.37	12.797%	$113.2143	$113.21	$113.20	$113.20
Purchase #4	$78.69	13.783%	$89.5358	$89.54	$89.55	$89.50
Purchase #5	$248.43	10.789%	$275.2331	$275.23	$275.25	$275.20
Purchase #6	$79.71	7.728%	$85.87	$85.87	$85.85	$85.90
Purchase #7	$137.53	13.870%	$156.6054	$156.61	$156.60	$156.60
7 purchase totals =	$932.39		$1,039.7395	$1,039.74	$1,039.75	$1,039.70