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 $44.76   13.593%   $50.8442   $50.84   $50.85   $50.80  
  Purchase #2 $244.32   6.686%   $260.6552   $260.66   $260.65   $260.70  
  Purchase #3 $33.49   7.336%   $35.9468   $35.95   $35.95   $35.90  
  Purchase #4 $78.81   8.743%   $85.7004   $85.70   $85.70   $85.70  
  Purchase #5 $161.89   11.234%   $180.0767   $180.08   $180.10   $180.10  
  Purchase #6 $152.85   12.391%   $171.7896   $171.79   $171.80   $171.80  
  Purchase #7 $152.85   8.552%   $165.9217   $165.92   $165.90   $165.90  
  7 purchase totals = $868.97       $950.9346   $950.94   $950.95   $950.90