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	$86.27	4.223%	$89.9132	$89.91	$89.90	$89.90
Purchase #2	$177.85	10.314%	$196.1934	$196.19	$196.20	$196.20
Purchase #3	$201.51	10.820%	$223.3134	$223.31	$223.30	$223.30
Purchase #4	$141.76	12.607%	$159.6317	$159.63	$159.65	$159.60
Purchase #5	$249.96	9.322%	$273.2613	$273.26	$273.25	$273.30
Purchase #6	$212.32	10.564%	$234.7495	$234.75	$234.75	$234.70
Purchase #7	$88.28	12.348%	$99.1808	$99.18	$99.20	$99.20
7 purchase totals =	$1,157.95		$1,276.2433	$1,276.23	$1,276.25	$1,276.20