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 $86.52   10.691%   $95.7699   $95.77   $95.75   $95.80  
  Purchase #2 $169.85   3.405%   $175.6334   $175.63   $175.65   $175.60  
  Purchase #3 $243.96   6.541%   $259.9174   $259.92   $259.90   $259.90  
  Purchase #4 $113.65   3.683%   $117.8357   $117.84   $117.85   $117.80  
  Purchase #5 $88.96   5.543%   $93.8911   $93.89   $93.90   $93.90  
  Purchase #6 $235.33   4.455%   $245.814   $245.81   $245.80   $245.80  
  Purchase #7 $10.52   9.178%   $11.4855   $11.49   $11.50   $11.50  
  7 purchase totals = $948.79       $1,000.3470   $1,000.35   $1,000.35   $1,000.30