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 $57.45   8.515%   $62.3419   $62.34   $62.35   $62.30  
  Purchase #2 $138.34   3.273%   $142.8679   $142.87   $142.85   $142.90  
  Purchase #3 $6.72   9.348%   $7.3482   $7.35   $7.35   $7.30  
  Purchase #4 $124.53   9.601%   $136.4861   $136.49   $136.50   $136.50  
  Purchase #5 $19.85   5.179%   $20.878   $20.88   $20.90   $20.90  
  Purchase #6 $201.66   12.292%   $226.448   $226.45   $226.45   $226.40  
  Purchase #7 $220.33   12.179%   $247.164   $247.16   $247.15   $247.20  
  7 purchase totals = $768.88       $843.5341   $843.54   $843.55   $843.50