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	$164.65	12.705%	$185.5688	$185.57	$185.55	$185.60
Purchase #2	$42.35	8.290%	$45.8608	$45.86	$45.85	$45.90
Purchase #3	$90.28	12.780%	$101.8178	$101.82	$101.80	$101.80
Purchase #4	$21.96	11.126%	$24.4033	$24.40	$24.40	$24.40
Purchase #5	$243.83	8.258%	$263.9655	$263.97	$263.95	$264.00
Purchase #6	$235.76	8.516%	$255.8373	$255.84	$255.85	$255.80
Purchase #7	$188.86	11.656%	$210.8735	$210.87	$210.85	$210.90
7 purchase totals =	$987.69		$1,088.3270	$1,088.33	$1,088.25	$1,088.40