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	$223.70	8.681%	$243.1194	$243.12	$243.10	$243.10
Purchase #2	$245.66	4.542%	$256.8179	$256.82	$256.80	$256.80
Purchase #3	$126.96	7.182%	$136.0783	$136.08	$136.10	$136.10
Purchase #4	$56.38	6.217%	$59.8851	$59.89	$59.90	$59.90
Purchase #5	$165.44	13.500%	$187.7744	$187.77	$187.75	$187.80
Purchase #6	$180.91	3.285%	$186.8529	$186.85	$186.85	$186.90
Purchase #7	$141.25	13.133%	$159.8004	$159.80	$159.80	$159.80
7 purchase totals =	$1,140.30		$1,230.3284	$1,230.33	$1,230.30	$1,230.40