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	$134.91	11.412%	$150.3059	$150.31	$150.30	$150.30
Purchase #2	$29.68	10.386%	$32.7626	$32.76	$32.75	$32.80
Purchase #3	$132.44	12.474%	$148.9606	$148.96	$148.95	$149.00
Purchase #4	$28.53	13.524%	$32.3884	$32.39	$32.40	$32.40
Purchase #5	$28.41	10.503%	$31.3939	$31.39	$31.40	$31.40
Purchase #6	$84.56	5.192%	$88.9504	$88.95	$88.95	$89.00
Purchase #7	$54.66	13.465%	$62.02	$62.02	$62.00	$62.00
7 purchase totals =	$493.19		$546.7818	$546.78	$546.75	$546.90