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 $49.81   10.517%   $55.0485   $55.05   $55.05   $55.00  
  Purchase #2 $68.80   12.755%   $77.5754   $77.58   $77.60   $77.60  
  Purchase #3 $174.63   13.821%   $198.7656   $198.77   $198.75   $198.80  
  Purchase #4 $198.33   9.122%   $216.4217   $216.42   $216.40   $216.40  
  Purchase #5 $67.54   9.772%   $74.14   $74.14   $74.15   $74.10  
  Purchase #6 $205.88   9.763%   $225.9801   $225.98   $226.00   $226.00  
  Purchase #7 $9.66   13.540%   $10.968   $10.97   $10.95   $11.00  
  7 purchase totals = $774.65       $858.8993   $858.91   $858.90   $858.90