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 $127.66   13.397%   $144.7626   $144.76   $144.75   $144.80  
  Purchase #2 $89.71   4.224%   $93.4994   $93.50   $93.50   $93.50  
  Purchase #3 $205.63   3.466%   $212.7571   $212.76   $212.75   $212.80  
  Purchase #4 $16.39   5.323%   $17.2624   $17.26   $17.25   $17.30  
  Purchase #5 $156.42   5.842%   $165.5581   $165.56   $165.55   $165.60  
  Purchase #6 $237.72   7.193%   $254.8192   $254.82   $254.80   $254.80  
  Purchase #7 $160.84   8.521%   $174.5452   $174.55   $174.55   $174.50  
  7 purchase totals = $994.37       $1,063.2040   $1,063.21   $1,063.15   $1,063.30