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	$73.80	6.812%	$78.8273	$78.83	$78.85	$78.80
Purchase #2	$80.77	11.379%	$89.9608	$89.96	$89.95	$90.00
Purchase #3	$136.54	11.253%	$151.9048	$151.90	$151.90	$151.90
Purchase #4	$235.84	9.417%	$258.0491	$258.05	$258.05	$258.00
Purchase #5	$61.65	5.867%	$65.267	$65.27	$65.25	$65.30
Purchase #6	$130.34	5.136%	$137.0343	$137.03	$137.05	$137.00
Purchase #7	$80.89	13.428%	$91.7519	$91.75	$91.75	$91.80
7 purchase totals =	$799.83		$872.7952	$872.79	$872.80	$872.80