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	$162.84	5.504%	$171.8027	$171.80	$171.80	$171.80
Purchase #2	$243.88	7.380%	$261.8783	$261.88	$261.90	$261.90
Purchase #3	$250.49	5.125%	$263.3276	$263.33	$263.35	$263.30
Purchase #4	$159.43	8.709%	$173.3148	$173.31	$173.30	$173.30
Purchase #5	$61.46	6.142%	$65.2349	$65.23	$65.25	$65.20
Purchase #6	$117.81	11.215%	$131.0224	$131.02	$131.00	$131.00
Purchase #7	$115.72	13.488%	$131.3283	$131.33	$131.35	$131.30
7 purchase totals =	$1,111.63		$1,197.9090	$1,197.90	$1,197.95	$1,197.80