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 $85.63   9.180%   $93.4908   $93.49   $93.50   $93.50  
  Purchase #2 $113.95   6.114%   $120.9169   $120.92   $120.90   $120.90  
  Purchase #3 $115.91   13.638%   $131.7178   $131.72   $131.70   $131.70  
  Purchase #4 $235.36   4.312%   $245.5087   $245.51   $245.50   $245.50  
  Purchase #5 $151.58   11.201%   $168.5585   $168.56   $168.55   $168.60  
  Purchase #6 $243.66   3.570%   $252.3587   $252.36   $252.35   $252.40  
  Purchase #7 $27.83   12.360%   $31.2698   $31.27   $31.25   $31.30  
  7 purchase totals = $973.92       $1,043.8212   $1,043.83   $1,043.75   $1,043.90