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 $103.70   10.264%   $114.3438   $114.34   $114.35   $114.30  
  Purchase #2 $57.59   4.151%   $59.9806   $59.98   $60.00   $60.00  
  Purchase #3 $12.44   12.349%   $13.9762   $13.98   $14.00   $14.00  
  Purchase #4 $244.83   8.260%   $265.053   $265.05   $265.05   $265.10  
  Purchase #5 $245.88   13.635%   $279.4057   $279.41   $279.40   $279.40  
  Purchase #6 $96.52   10.389%   $106.5475   $106.55   $106.55   $106.50  
  Purchase #7 $187.58   3.838%   $194.7793   $194.78   $194.80   $194.80  
  7 purchase totals = $948.54       $1,034.0861   $1,034.09   $1,034.15   $1,034.10