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	$250.29	3.358%	$258.6947	$258.69	$258.70	$258.70
Purchase #2	$82.38	8.695%	$89.5429	$89.54	$89.55	$89.50
Purchase #3	$92.64	10.872%	$102.7118	$102.71	$102.70	$102.70
Purchase #4	$175.71	6.654%	$187.4017	$187.40	$187.40	$187.40
Purchase #5	$153.45	9.427%	$167.9157	$167.92	$167.90	$167.90
Purchase #6	$172.48	4.812%	$180.7797	$180.78	$180.80	$180.80
Purchase #7	$98.26	6.330%	$104.4799	$104.48	$104.50	$104.50
7 purchase totals =	$1,025.21		$1,091.5264	$1,091.52	$1,091.55	$1,091.50