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 $64.51   3.471%   $66.7491   $66.75   $66.75   $66.70  
  Purchase #2 $111.69   6.116%   $118.521   $118.52   $118.50   $118.50  
  Purchase #3 $54.89   9.248%   $59.9662   $59.97   $59.95   $60.00  
  Purchase #4 $35.77   4.621%   $37.4229   $37.42   $37.40   $37.40  
  Purchase #5 $204.25   7.226%   $219.0091   $219.01   $219.00   $219.00  
  Purchase #6 $105.26   3.195%   $108.6231   $108.62   $108.60   $108.60  
  Purchase #7 $137.58   13.113%   $155.6209   $155.62   $155.60   $155.60  
  7 purchase totals = $713.95       $765.9123   $765.91   $765.80   $765.80