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	$90.63	13.162%	$102.5587	$102.56	$102.55	$102.60
Purchase #2	$78.74	13.651%	$89.4888	$89.49	$89.50	$89.50
Purchase #3	$35.37	7.316%	$37.9577	$37.96	$37.95	$38.00
Purchase #4	$180.41	8.316%	$195.4129	$195.41	$195.40	$195.40
Purchase #5	$59.76	3.592%	$61.9066	$61.91	$61.90	$61.90
Purchase #6	$247.83	9.218%	$270.675	$270.68	$270.70	$270.70
Purchase #7	$81.50	7.874%	$87.9173	$87.92	$87.90	$87.90
7 purchase totals =	$774.24		$845.9170	$845.93	$845.90	$846.00