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	$28.77	10.846%	$31.8904	$31.89	$31.90	$31.90
Purchase #2	$71.53	7.317%	$76.7639	$76.76	$76.75	$76.80
Purchase #3	$13.89	5.507%	$14.6549	$14.65	$14.65	$14.70
Purchase #4	$228.64	9.457%	$250.2625	$250.26	$250.25	$250.30
Purchase #5	$106.75	11.598%	$119.1309	$119.13	$119.15	$119.10
Purchase #6	$236.78	11.707%	$264.4998	$264.50	$264.50	$264.50
Purchase #7	$242.38	12.796%	$273.3949	$273.39	$273.40	$273.40
7 purchase totals =	$928.74		$1,030.5973	$1,030.58	$1,030.60	$1,030.70