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 $59.94   5.493%   $63.2325   $63.23   $63.25   $63.20  
  Purchase #2 $10.33   4.595%   $10.8047   $10.80   $10.80   $10.80  
  Purchase #3 $5.95   6.226%   $6.3204   $6.32   $6.30   $6.30  
  Purchase #4 $136.87   8.822%   $148.9447   $148.94   $148.95   $148.90  
  Purchase #5 $243.70   13.174%   $275.805   $275.81   $275.80   $275.80  
  Purchase #6 $219.28   12.531%   $246.758   $246.76   $246.75   $246.80  
  Purchase #7 $125.88   7.164%   $134.898   $134.90   $134.90   $134.90  
  7 purchase totals = $801.95       $886.7633   $886.76   $886.75   $886.70