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	$181.37	4.231%	$189.0438	$189.04	$189.05	$189.00
Purchase #2	$110.36	3.809%	$114.5636	$114.56	$114.55	$114.60
Purchase #3	$167.52	7.419%	$179.9483	$179.95	$179.95	$179.90
Purchase #4	$157.64	10.455%	$174.1213	$174.12	$174.10	$174.10
Purchase #5	$74.76	4.742%	$78.3051	$78.31	$78.30	$78.30
Purchase #6	$114.50	9.600%	$125.492	$125.49	$125.50	$125.50
Purchase #7	$39.58	7.332%	$42.482	$42.48	$42.50	$42.50
7 purchase totals =	$845.73		$903.9561	$903.95	$903.95	$903.90