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	$245.80	12.167%	$275.7065	$275.71	$275.70	$275.70
Purchase #2	$52.57	12.823%	$59.3111	$59.31	$59.30	$59.30
Purchase #3	$231.50	6.873%	$247.411	$247.41	$247.40	$247.40
Purchase #4	$209.54	6.561%	$223.2879	$223.29	$223.30	$223.30
Purchase #5	$52.86	8.695%	$57.4562	$57.46	$57.45	$57.50
Purchase #6	$215.54	6.479%	$229.5048	$229.50	$229.50	$229.50
Purchase #7	$82.29	13.751%	$93.6057	$93.61	$93.60	$93.60
7 purchase totals =	$1,090.10		$1,186.2832	$1,186.29	$1,186.25	$1,186.30