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	$133.78	5.698%	$141.4028	$141.40	$141.40	$141.40
Purchase #2	$106.61	7.158%	$114.2411	$114.24	$114.25	$114.20
Purchase #3	$112.41	10.398%	$124.0984	$124.10	$124.10	$124.10
Purchase #4	$78.63	13.629%	$89.3465	$89.35	$89.35	$89.30
Purchase #5	$77.87	7.324%	$83.5732	$83.57	$83.55	$83.60
Purchase #6	$94.98	6.238%	$100.9049	$100.90	$100.90	$100.90
Purchase #7	$87.67	10.338%	$96.7333	$96.73	$96.75	$96.70
7 purchase totals =	$691.95		$750.3002	$750.29	$750.30	$750.20