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	$245.46	11.354%	$273.3295	$273.33	$273.35	$273.30
Purchase #2	$247.49	6.869%	$264.4901	$264.49	$264.50	$264.50
Purchase #3	$152.27	10.870%	$168.8217	$168.82	$168.80	$168.80
Purchase #4	$182.73	5.500%	$192.7802	$192.78	$192.80	$192.80
Purchase #5	$124.58	4.437%	$130.1076	$130.11	$130.10	$130.10
Purchase #6	$43.89	6.869%	$46.9048	$46.90	$46.90	$46.90
Purchase #7	$19.94	7.570%	$21.4495	$21.45	$21.45	$21.40
7 purchase totals =	$1,016.36		$1,097.8834	$1,097.88	$1,097.90	$1,097.80