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 $76.93   11.390%   $85.6923   $85.69   $85.70   $85.70  
  Purchase #2 $55.47   9.149%   $60.545   $60.55   $60.55   $60.50  
  Purchase #3 $56.69   12.340%   $63.6855   $63.69   $63.70   $63.70  
  Purchase #4 $235.76   9.221%   $257.4994   $257.50   $257.50   $257.50  
  Purchase #5 $35.85   10.278%   $39.5347   $39.53   $39.55   $39.50  
  Purchase #6 $146.67   6.140%   $155.6755   $155.68   $155.70   $155.70  
  Purchase #7 $85.61   4.725%   $89.6551   $89.66   $89.65   $89.70  
  7 purchase totals = $692.98       $752.2875   $752.30   $752.35   $752.30