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 $67.29   3.521%   $69.6593   $69.66   $69.65   $69.70  
  Purchase #2 $230.40   9.715%   $252.7834   $252.78   $252.80   $252.80  
  Purchase #3 $82.72   4.169%   $86.1686   $86.17   $86.15   $86.20  
  Purchase #4 $215.98   5.726%   $228.347   $228.35   $228.35   $228.30  
  Purchase #5 $119.86   12.631%   $134.9995   $135.00   $135.00   $135.00  
  Purchase #6 $50.96   3.816%   $52.9046   $52.90   $52.90   $52.90  
  Purchase #7 $151.55   12.388%   $170.324   $170.32   $170.30   $170.30  
  7 purchase totals = $918.76       $995.1864   $995.18   $995.15   $995.20