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	$230.25	5.770%	$243.5354	$243.54	$243.55	$243.50
Purchase #2	$183.98	9.430%	$201.3293	$201.33	$201.35	$201.30
Purchase #3	$23.73	5.497%	$25.0344	$25.03	$25.05	$25.00
Purchase #4	$65.39	12.369%	$73.4781	$73.48	$73.50	$73.50
Purchase #5	$175.31	3.768%	$181.9157	$181.92	$181.90	$181.90
Purchase #6	$83.41	7.528%	$89.6891	$89.69	$89.70	$89.70
Purchase #7	$118.74	7.662%	$127.8379	$127.84	$127.85	$127.80
7 purchase totals =	$880.81		$942.8199	$942.83	$942.90	$942.70