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	$71.85	8.437%	$77.912	$77.91	$77.90	$77.90
Purchase #2	$106.72	6.422%	$113.5736	$113.57	$113.55	$113.60
Purchase #3	$31.86	10.444%	$35.1875	$35.19	$35.20	$35.20
Purchase #4	$60.54	12.172%	$67.9089	$67.91	$67.90	$67.90
Purchase #5	$123.51	12.830%	$139.3563	$139.36	$139.35	$139.40
Purchase #6	$75.38	8.751%	$81.9765	$81.98	$82.00	$82.00
Purchase #7	$245.44	11.543%	$273.7711	$273.77	$273.75	$273.80
7 purchase totals =	$715.30		$789.6859	$789.69	$789.65	$789.80