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	$81.62	9.359%	$89.2588	$89.26	$89.25	$89.30
Purchase #2	$194.81	6.130%	$206.7519	$206.75	$206.75	$206.80
Purchase #3	$32.95	6.813%	$35.1949	$35.19	$35.20	$35.20
Purchase #4	$82.98	8.361%	$89.918	$89.92	$89.90	$89.90
Purchase #5	$31.93	5.557%	$33.7044	$33.70	$33.70	$33.70
Purchase #6	$237.98	5.165%	$250.2717	$250.27	$250.25	$250.30
Purchase #7	$83.69	3.268%	$86.425	$86.43	$86.45	$86.40
7 purchase totals =	$745.96		$791.5247	$791.52	$791.50	$791.60