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	$236.31	6.360%	$251.3393	$251.34	$251.35	$251.30
Purchase #2	$165.82	12.597%	$186.7083	$186.71	$186.70	$186.70
Purchase #3	$53.25	7.619%	$57.3071	$57.31	$57.30	$57.30
Purchase #4	$157.36	9.178%	$171.8025	$171.80	$171.80	$171.80
Purchase #5	$85.37	7.152%	$91.4757	$91.48	$91.50	$91.50
Purchase #6	$72.67	8.557%	$78.8884	$78.89	$78.90	$78.90
Purchase #7	$63.38	10.177%	$69.8302	$69.83	$69.85	$69.80
7 purchase totals =	$834.16		$907.3515	$907.36	$907.40	$907.30