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	$40.76	3.309%	$42.1087	$42.11	$42.10	$42.10
Purchase #2	$64.26	12.219%	$72.1119	$72.11	$72.10	$72.10
Purchase #3	$88.57	11.210%	$98.4987	$98.50	$98.50	$98.50
Purchase #4	$60.31	6.475%	$64.2151	$64.22	$64.20	$64.20
Purchase #5	$53.29	10.199%	$58.725	$58.73	$58.75	$58.70
Purchase #6	$52.48	8.398%	$56.8873	$56.89	$56.90	$56.90
Purchase #7	$118.73	12.800%	$133.9274	$133.93	$133.95	$133.90
7 purchase totals =	$478.40		$526.4741	$526.49	$526.50	$526.40