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	$67.72	6.811%	$72.3324	$72.33	$72.35	$72.30
Purchase #2	$245.77	3.330%	$253.9541	$253.95	$253.95	$254.00
Purchase #3	$20.87	10.433%	$23.0474	$23.05	$23.05	$23.00
Purchase #4	$80.49	11.770%	$89.9637	$89.96	$89.95	$90.00
Purchase #5	$42.66	7.281%	$45.7661	$45.77	$45.75	$45.80
Purchase #6	$227.49	7.132%	$243.7146	$243.71	$243.70	$243.70
Purchase #7	$159.38	5.459%	$168.0806	$168.08	$168.10	$168.10
7 purchase totals =	$844.38		$896.8589	$896.85	$896.85	$896.90