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 $162.87   6.841%   $174.0119   $174.01   $174.00   $174.00  
  Purchase #2 $246.55   12.314%   $276.9102   $276.91   $276.90   $276.90  
  Purchase #3 $165.79   5.308%   $174.5901   $174.59   $174.60   $174.60  
  Purchase #4 $67.77   13.290%   $76.7766   $76.78   $76.80   $76.80  
  Purchase #5 $21.82   11.291%   $24.2837   $24.28   $24.30   $24.30  
  Purchase #6 $76.32   10.835%   $84.5893   $84.59   $84.60   $84.60  
  Purchase #7 $52.27   8.398%   $56.6596   $56.66   $56.65   $56.70  
  7 purchase totals = $793.39       $867.8214   $867.82   $867.85   $867.90