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	$234.77	6.817%	$250.7743	$250.77	$250.75	$250.80
Purchase #2	$213.86	7.443%	$229.7776	$229.78	$229.80	$229.80
Purchase #3	$35.31	12.366%	$39.6764	$39.68	$39.70	$39.70
Purchase #4	$162.46	5.785%	$171.8583	$171.86	$171.85	$171.90
Purchase #5	$240.86	11.838%	$269.373	$269.37	$269.35	$269.40
Purchase #6	$37.69	13.873%	$42.9187	$42.92	$42.90	$42.90
Purchase #7	$137.73	6.573%	$146.783	$146.78	$146.80	$146.80
7 purchase totals =	$1,062.68		$1,151.1613	$1,151.16	$1,151.15	$1,151.30