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 $70.49   7.726%   $75.9361   $75.94   $75.95   $75.90  
  Purchase #2 $19.91   7.818%   $21.4666   $21.47   $21.45   $21.50  
  Purchase #3 $161.94   12.867%   $182.7768   $182.78   $182.80   $182.80  
  Purchase #4 $63.77   7.630%   $68.6357   $68.64   $68.65   $68.60  
  Purchase #5 $57.55   8.695%   $62.554   $62.55   $62.55   $62.60  
  Purchase #6 $190.36   6.655%   $203.0285   $203.03   $203.05   $203.00  
  Purchase #7 $142.96   12.734%   $161.1645   $161.16   $161.15   $161.20  
  7 purchase totals = $706.98       $775.5622   $775.57   $775.60   $775.60