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 $52.70   12.444%   $59.258   $59.26   $59.25   $59.30  
  Purchase #2 $56.71   8.672%   $61.6279   $61.63   $61.65   $61.60  
  Purchase #3 $247.33   11.659%   $276.1662   $276.17   $276.15   $276.20  
  Purchase #4 $33.72   6.518%   $35.9179   $35.92   $35.90   $35.90  
  Purchase #5 $233.29   8.319%   $252.6974   $252.70   $252.70   $252.70  
  Purchase #6 $47.31   6.343%   $50.3109   $50.31   $50.30   $50.30  
  Purchase #7 $26.63   3.570%   $27.5807   $27.58   $27.60   $27.60  
  7 purchase totals = $697.69       $763.5590   $763.57   $763.55   $763.60