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	$80.48	5.753%	$85.11	$85.11	$85.10	$85.10
Purchase #2	$215.57	6.643%	$229.8903	$229.89	$229.90	$229.90
Purchase #3	$206.30	12.541%	$232.1721	$232.17	$232.15	$232.20
Purchase #4	$235.81	6.316%	$250.7038	$250.70	$250.70	$250.70
Purchase #5	$32.72	13.184%	$37.0338	$37.03	$37.05	$37.00
Purchase #6	$47.66	5.137%	$50.1083	$50.11	$50.10	$50.10
Purchase #7	$199.36	3.577%	$206.4911	$206.49	$206.50	$206.50
7 purchase totals =	$1,017.90		$1,091.5094	$1,091.50	$1,091.50	$1,091.50