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	$209.84	6.165%	$222.7766	$222.78	$222.80	$222.80
Purchase #2	$155.66	10.444%	$171.9171	$171.92	$171.90	$171.90
Purchase #3	$188.70	5.148%	$198.4143	$198.41	$198.40	$198.40
Purchase #4	$31.91	9.133%	$34.8243	$34.82	$34.80	$34.80
Purchase #5	$96.31	10.189%	$106.123	$106.12	$106.10	$106.10
Purchase #6	$53.82	10.357%	$59.3941	$59.39	$59.40	$59.40
Purchase #7	$156.78	5.381%	$165.2163	$165.22	$165.20	$165.20
7 purchase totals =	$893.02		$958.6657	$958.66	$958.60	$958.60