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	$47.93	8.746%	$52.122	$52.12	$52.10	$52.10
Purchase #2	$99.72	10.234%	$109.9253	$109.93	$109.95	$109.90
Purchase #3	$47.34	12.276%	$53.1515	$53.15	$53.15	$53.20
Purchase #4	$35.63	6.424%	$37.9189	$37.92	$37.90	$37.90
Purchase #5	$68.90	12.507%	$77.5173	$77.52	$77.50	$77.50
Purchase #6	$186.81	13.589%	$212.1956	$212.20	$212.20	$212.20
Purchase #7	$131.46	7.572%	$141.4142	$141.41	$141.40	$141.40
7 purchase totals =	$617.79		$684.2448	$684.25	$684.20	$684.20