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	$157.55	8.110%	$170.3273	$170.33	$170.35	$170.30
Purchase #2	$74.84	9.614%	$82.0351	$82.04	$82.05	$82.00
Purchase #3	$100.46	3.146%	$103.6205	$103.62	$103.60	$103.60
Purchase #4	$215.84	9.358%	$236.0383	$236.04	$236.05	$236.00
Purchase #5	$127.46	9.323%	$139.3431	$139.34	$139.35	$139.30
Purchase #6	$242.57	10.850%	$268.8888	$268.89	$268.90	$268.90
Purchase #7	$17.97	11.474%	$20.0319	$20.03	$20.05	$20.00
7 purchase totals =	$936.69		$1,020.2850	$1,020.29	$1,020.35	$1,020.10