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 $116.98   8.337%   $126.7326   $126.73   $126.75   $126.70  
  Purchase #2 $67.31   5.753%   $71.1823   $71.18   $71.20   $71.20  
  Purchase #3 $95.63   10.357%   $105.5344   $105.53   $105.55   $105.50  
  Purchase #4 $79.98   11.595%   $89.2537   $89.25   $89.25   $89.30  
  Purchase #5 $177.49   6.587%   $189.1813   $189.18   $189.20   $189.20  
  Purchase #6 $58.69   7.316%   $62.9838   $62.98   $63.00   $63.00  
  Purchase #7 $160.59   13.381%   $182.0785   $182.08   $182.10   $182.10  
  7 purchase totals = $756.67       $826.9466   $826.93   $827.05   $827.00