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 $227.89   11.807%   $254.797   $254.80   $254.80   $254.80  
  Purchase #2 $61.47   12.167%   $68.9491   $68.95   $68.95   $68.90  
  Purchase #3 $77.94   5.838%   $82.4901   $82.49   $82.50   $82.50  
  Purchase #4 $82.52   12.182%   $92.5726   $92.57   $92.55   $92.60  
  Purchase #5 $144.40   8.384%   $156.5065   $156.51   $156.50   $156.50  
  Purchase #6 $179.75   3.265%   $185.6188   $185.62   $185.60   $185.60  
  Purchase #7 $63.59   7.258%   $68.2054   $68.21   $68.20   $68.20  
  7 purchase totals = $837.56       $909.1395   $909.15   $909.10   $909.10