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 $208.52   9.732%   $228.8132   $228.81   $228.80   $228.80  
  Purchase #2 $154.72   13.701%   $175.9182   $175.92   $175.90   $175.90  
  Purchase #3 $20.64   8.521%   $22.3987   $22.40   $22.40   $22.40  
  Purchase #4 $216.74   8.611%   $235.4035   $235.40   $235.40   $235.40  
  Purchase #5 $102.45   10.860%   $113.5761   $113.58   $113.60   $113.60  
  Purchase #6 $9.86   5.231%   $10.3758   $10.38   $10.40   $10.40  
  Purchase #7 $248.30   4.646%   $259.836   $259.84   $259.85   $259.80  
  7 purchase totals = $961.23       $1,046.3215   $1,046.33   $1,046.35   $1,046.30