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	$165.34	5.788%	$174.9099	$174.91	$174.90	$174.90
Purchase #2	$117.80	6.404%	$125.3439	$125.34	$125.35	$125.30
Purchase #3	$131.49	12.206%	$147.5397	$147.54	$147.55	$147.50
Purchase #4	$136.61	3.404%	$141.2602	$141.26	$141.25	$141.30
Purchase #5	$31.50	11.548%	$35.1376	$35.14	$35.15	$35.10
Purchase #6	$86.69	4.298%	$90.4159	$90.42	$90.40	$90.40
Purchase #7	$53.90	8.820%	$58.654	$58.65	$58.65	$58.70
7 purchase totals =	$723.33		$773.2612	$773.26	$773.25	$773.20