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	$129.54	3.169%	$133.6451	$133.65	$133.65	$133.60
Purchase #2	$85.35	8.839%	$92.8941	$92.89	$92.90	$92.90
Purchase #3	$75.56	12.728%	$85.1773	$85.18	$85.20	$85.20
Purchase #4	$238.37	11.554%	$265.9113	$265.91	$265.90	$265.90
Purchase #5	$212.26	6.160%	$225.3352	$225.34	$225.35	$225.30
Purchase #6	$86.84	5.166%	$91.3262	$91.33	$91.35	$91.30
Purchase #7	$139.57	7.550%	$150.1075	$150.11	$150.10	$150.10
7 purchase totals =	$967.49		$1,044.3967	$1,044.41	$1,044.45	$1,044.30