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	$235.40	6.415%	$250.5009	$250.50	$250.50	$250.50
Purchase #2	$65.57	12.323%	$73.6502	$73.65	$73.65	$73.70
Purchase #3	$60.87	11.130%	$67.6448	$67.64	$67.65	$67.60
Purchase #4	$147.26	11.850%	$164.7103	$164.71	$164.70	$164.70
Purchase #5	$25.34	13.126%	$28.6661	$28.67	$28.65	$28.70
Purchase #6	$59.36	13.668%	$67.4733	$67.47	$67.45	$67.50
Purchase #7	$167.66	8.655%	$182.171	$182.17	$182.15	$182.20
7 purchase totals =	$761.46		$834.8166	$834.81	$834.75	$834.90