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 $24.47   10.516%   $27.0433   $27.04   $27.05   $27.00  
  Purchase #2 $113.87   4.759%   $119.2891   $119.29   $119.30   $119.30  
  Purchase #3 $221.72   12.620%   $249.7011   $249.70   $249.70   $249.70  
  Purchase #4 $210.74   6.387%   $224.2   $224.20   $224.20   $224.20  
  Purchase #5 $223.92   12.831%   $252.6512   $252.65   $252.65   $252.70  
  Purchase #6 $232.30   13.870%   $264.52   $264.52   $264.50   $264.50  
  Purchase #7 $208.72   8.236%   $225.9102   $225.91   $225.90   $225.90  
  7 purchase totals = $1,235.74       $1,363.3149   $1,363.31   $1,363.30   $1,363.30