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	$53.34	10.803%	$59.1023	$59.10	$59.10	$59.10
Purchase #2	$149.63	4.319%	$156.0925	$156.09	$156.10	$156.10
Purchase #3	$93.33	6.477%	$99.375	$99.38	$99.40	$99.40
Purchase #4	$67.96	4.655%	$71.1235	$71.12	$71.10	$71.10
Purchase #5	$14.62	3.576%	$15.1428	$15.14	$15.15	$15.10
Purchase #6	$82.88	7.589%	$89.1698	$89.17	$89.15	$89.20
Purchase #7	$137.31	3.765%	$142.4797	$142.48	$142.50	$142.50
7 purchase totals =	$599.07		$632.4856	$632.48	$632.50	$632.50