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	$137.96	7.822%	$148.7512	$148.75	$148.75	$148.80
Purchase #2	$235.46	12.253%	$264.3109	$264.31	$264.30	$264.30
Purchase #3	$118.42	7.730%	$127.5739	$127.57	$127.55	$127.60
Purchase #4	$209.47	11.857%	$234.3069	$234.31	$234.30	$234.30
Purchase #5	$95.40	6.272%	$101.3835	$101.38	$101.40	$101.40
Purchase #6	$245.61	9.760%	$269.5815	$269.58	$269.60	$269.60
Purchase #7	$223.37	12.312%	$250.8713	$250.87	$250.85	$250.90
7 purchase totals =	$1,265.69		$1,396.7792	$1,396.77	$1,396.75	$1,396.90