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	$131.39	12.556%	$147.8873	$147.89	$147.90	$147.90
Purchase #2	$149.49	8.460%	$162.1369	$162.14	$162.15	$162.10
Purchase #3	$96.28	3.353%	$99.5083	$99.51	$99.50	$99.50
Purchase #4	$150.76	5.773%	$159.4634	$159.46	$159.45	$159.50
Purchase #5	$79.93	3.726%	$82.9082	$82.91	$82.90	$82.90
Purchase #6	$17.87	13.732%	$20.3239	$20.32	$20.30	$20.30
Purchase #7	$104.72	8.386%	$113.5018	$113.50	$113.50	$113.50
7 purchase totals =	$730.44		$785.7298	$785.73	$785.70	$785.70