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	$70.76	11.529%	$78.9179	$78.92	$78.90	$78.90
Purchase #2	$67.68	6.292%	$71.9384	$71.94	$71.95	$71.90
Purchase #3	$243.27	10.316%	$268.3657	$268.37	$268.35	$268.40
Purchase #4	$72.63	3.453%	$75.1379	$75.14	$75.15	$75.10
Purchase #5	$158.87	12.606%	$178.8972	$178.90	$178.90	$178.90
Purchase #6	$88.79	4.642%	$92.9116	$92.91	$92.90	$92.90
Purchase #7	$81.58	12.586%	$91.8477	$91.85	$91.85	$91.80
7 purchase totals =	$783.58		$858.0164	$858.03	$858.00	$857.90