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	$39.48	6.506%	$42.0486	$42.05	$42.05	$42.00
Purchase #2	$79.56	13.666%	$90.4327	$90.43	$90.45	$90.40
Purchase #3	$238.45	12.347%	$267.8914	$267.89	$267.90	$267.90
Purchase #4	$223.33	5.350%	$235.2782	$235.28	$235.30	$235.30
Purchase #5	$65.32	9.109%	$71.27	$71.27	$71.25	$71.30
Purchase #6	$129.95	4.787%	$136.1707	$136.17	$136.15	$136.20
Purchase #7	$190.67	9.673%	$209.1135	$209.11	$209.10	$209.10
7 purchase totals =	$966.76		$1,052.2051	$1,052.20	$1,052.20	$1,052.20