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	$111.31	10.699%	$123.2191	$123.22	$123.20	$123.20
Purchase #2	$89.53	6.465%	$95.3181	$95.32	$95.30	$95.30
Purchase #3	$88.62	12.282%	$99.5043	$99.50	$99.50	$99.50
Purchase #4	$98.49	10.765%	$109.0924	$109.09	$109.10	$109.10
Purchase #5	$107.36	7.575%	$115.4925	$115.49	$115.50	$115.50
Purchase #6	$183.57	3.218%	$189.4773	$189.48	$189.50	$189.50
Purchase #7	$188.58	3.171%	$194.5599	$194.56	$194.55	$194.60
7 purchase totals =	$867.46		$926.6636	$926.66	$926.65	$926.70