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	$122.96	5.354%	$129.5433	$129.54	$129.55	$129.50
Purchase #2	$159.89	6.424%	$170.1613	$170.16	$170.15	$170.20
Purchase #3	$38.55	13.782%	$43.863	$43.86	$43.85	$43.90
Purchase #4	$99.83	3.701%	$103.5247	$103.52	$103.50	$103.50
Purchase #5	$79.57	3.200%	$82.1162	$82.12	$82.10	$82.10
Purchase #6	$235.31	4.772%	$246.539	$246.54	$246.55	$246.50
Purchase #7	$149.94	4.216%	$156.2615	$156.26	$156.25	$156.30
7 purchase totals =	$886.05		$932.0090	$932.00	$931.95	$932.00