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 $56.78   12.535%   $63.8974   $63.90   $63.90   $63.90  
  Purchase #2 $39.58   9.483%   $43.3334   $43.33   $43.35   $43.30  
  Purchase #3 $157.47   3.816%   $163.4791   $163.48   $163.50   $163.50  
  Purchase #4 $248.83   3.432%   $257.3698   $257.37   $257.35   $257.40  
  Purchase #5 $188.25   3.588%   $195.0044   $195.00   $195.00   $195.00  
  Purchase #6 $59.30   8.484%   $64.331   $64.33   $64.35   $64.30  
  Purchase #7 $170.74   10.182%   $188.1247   $188.12   $188.10   $188.10  
  7 purchase totals = $920.95       $975.5398   $975.53   $975.55   $975.50