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	$36.46	3.273%	$37.6533	$37.65	$37.65	$37.70
Purchase #2	$191.89	9.257%	$209.6533	$209.65	$209.65	$209.70
Purchase #3	$225.43	6.467%	$240.0086	$240.01	$240.00	$240.00
Purchase #4	$93.68	6.281%	$99.564	$99.56	$99.55	$99.60
Purchase #5	$113.65	3.479%	$117.6039	$117.60	$117.60	$117.60
Purchase #6	$77.39	8.299%	$83.8126	$83.81	$83.80	$83.80
Purchase #7	$43.78	6.538%	$46.6423	$46.64	$46.65	$46.60
7 purchase totals =	$782.28		$834.9380	$834.92	$834.90	$835.00