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	$84.28	6.512%	$89.7683	$89.77	$89.75	$89.80
Purchase #2	$239.65	4.441%	$250.2929	$250.29	$250.30	$250.30
Purchase #3	$27.76	13.423%	$31.4862	$31.49	$31.50	$31.50
Purchase #4	$80.61	11.106%	$89.5625	$89.56	$89.55	$89.60
Purchase #5	$156.52	10.377%	$172.7621	$172.76	$172.75	$172.80
Purchase #6	$164.73	11.839%	$184.2324	$184.23	$184.25	$184.20
Purchase #7	$82.27	4.432%	$85.9162	$85.92	$85.90	$85.90
7 purchase totals =	$835.82		$904.0206	$904.02	$904.00	$904.10