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 $206.97   5.182%   $217.6952   $217.70   $217.70   $217.70  
  Purchase #2 $174.89   8.839%   $190.3485   $190.35   $190.35   $190.30  
  Purchase #3 $232.51   6.219%   $246.9698   $246.97   $246.95   $247.00  
  Purchase #4 $8.91   9.446%   $9.7516   $9.75   $9.75   $9.80  
  Purchase #5 $180.76   9.797%   $198.4691   $198.47   $198.45   $198.50  
  Purchase #6 $133.82   7.513%   $143.8739   $143.87   $143.85   $143.90  
  Purchase #7 $34.68   8.623%   $37.6705   $37.67   $37.65   $37.70  
  7 purchase totals = $972.54       $1,044.7786   $1,044.78   $1,044.70   $1,044.90