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	$213.43	6.790%	$227.9219	$227.92	$227.90	$227.90
Purchase #2	$68.47	11.512%	$76.3523	$76.35	$76.35	$76.40
Purchase #3	$188.49	4.388%	$196.7609	$196.76	$196.75	$196.80
Purchase #4	$140.58	11.184%	$156.3025	$156.30	$156.30	$156.30
Purchase #5	$87.57	3.167%	$90.3433	$90.34	$90.35	$90.30
Purchase #6	$75.25	4.817%	$78.8748	$78.87	$78.85	$78.90
Purchase #7	$21.51	8.317%	$23.299	$23.30	$23.30	$23.30
7 purchase totals =	$795.30		$849.8547	$849.84	$849.80	$849.90