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 $106.44   12.641%   $119.8951   $119.90   $119.90   $119.90  
  Purchase #2 $13.52   8.425%   $14.6591   $14.66   $14.65   $14.70  
  Purchase #3 $78.92   7.538%   $84.869   $84.87   $84.85   $84.90  
  Purchase #4 $61.45   13.542%   $69.7716   $69.77   $69.75   $69.80  
  Purchase #5 $195.34   3.527%   $202.2296   $202.23   $202.25   $202.20  
  Purchase #6 $91.95   9.858%   $101.0144   $101.01   $101.00   $101.00  
  Purchase #7 $228.69   10.578%   $252.8808   $252.88   $252.90   $252.90  
  7 purchase totals = $776.31       $845.3196   $845.32   $845.30   $845.40