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	$50.62	6.676%	$53.9994	$54.00	$54.00	$54.00
Purchase #2	$134.81	11.872%	$150.8146	$150.81	$150.80	$150.80
Purchase #3	$84.93	13.445%	$96.3488	$96.35	$96.35	$96.30
Purchase #4	$90.93	4.353%	$94.8882	$94.89	$94.90	$94.90
Purchase #5	$151.91	13.145%	$171.8786	$171.88	$171.90	$171.90
Purchase #6	$122.27	7.148%	$131.0099	$131.01	$131.00	$131.00
Purchase #7	$110.84	6.844%	$118.4259	$118.43	$118.45	$118.40
7 purchase totals =	$746.31		$817.3654	$817.37	$817.40	$817.30