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	$121.83	5.689%	$128.7609	$128.76	$128.75	$128.80
Purchase #2	$29.57	12.118%	$33.1533	$33.15	$33.15	$33.20
Purchase #3	$96.27	13.653%	$109.4137	$109.41	$109.40	$109.40
Purchase #4	$243.30	3.130%	$250.9153	$250.92	$250.90	$250.90
Purchase #5	$89.65	6.220%	$95.2262	$95.23	$95.25	$95.20
Purchase #6	$7.28	8.839%	$7.9235	$7.92	$7.90	$7.90
Purchase #7	$180.69	9.344%	$197.5737	$197.57	$197.55	$197.60
7 purchase totals =	$768.59		$822.9666	$822.96	$822.90	$823.00