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	$155.44	6.207%	$165.0882	$165.09	$165.10	$165.10
Purchase #2	$168.41	9.129%	$183.7841	$183.78	$183.80	$183.80
Purchase #3	$84.98	7.341%	$91.2184	$91.22	$91.20	$91.20
Purchase #4	$98.80	11.710%	$110.3695	$110.37	$110.35	$110.40
Purchase #5	$179.33	9.311%	$196.0274	$196.03	$196.05	$196.00
Purchase #6	$60.89	7.781%	$65.6279	$65.63	$65.65	$65.60
Purchase #7	$78.48	5.736%	$82.9816	$82.98	$83.00	$83.00
7 purchase totals =	$826.33		$895.0971	$895.10	$895.15	$895.10