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	$100.34	9.683%	$110.0559	$110.06	$110.05	$110.10
Purchase #2	$156.38	3.800%	$162.3224	$162.32	$162.30	$162.30
Purchase #3	$186.63	13.187%	$211.2409	$211.24	$211.25	$211.20
Purchase #4	$54.56	6.799%	$58.2695	$58.27	$58.25	$58.30
Purchase #5	$197.76	12.532%	$222.5433	$222.54	$222.55	$222.50
Purchase #6	$22.91	10.561%	$25.3295	$25.33	$25.35	$25.30
Purchase #7	$38.81	10.645%	$42.9413	$42.94	$42.95	$42.90
7 purchase totals =	$757.39		$832.7028	$832.70	$832.70	$832.60