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	$165.46	8.266%	$179.1369	$179.14	$179.15	$179.10
Purchase #2	$80.57	6.645%	$85.9239	$85.92	$85.90	$85.90
Purchase #3	$159.76	9.862%	$175.5155	$175.52	$175.50	$175.50
Purchase #4	$221.38	8.460%	$240.1087	$240.11	$240.10	$240.10
Purchase #5	$78.93	13.274%	$89.4072	$89.41	$89.40	$89.40
Purchase #6	$82.36	6.430%	$87.6557	$87.66	$87.65	$87.70
Purchase #7	$64.97	9.205%	$70.9505	$70.95	$70.95	$71.00
7 purchase totals =	$853.43		$928.6984	$928.71	$928.65	$928.70