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 $25.46   4.596%   $26.6301   $26.63   $26.65   $26.60  
  Purchase #2 $232.55   3.690%   $241.1311   $241.13   $241.15   $241.10  
  Purchase #3 $217.66   3.352%   $224.956   $224.96   $224.95   $225.00  
  Purchase #4 $239.41   5.119%   $251.6654   $251.67   $251.65   $251.70  
  Purchase #5 $49.34   3.458%   $51.0462   $51.05   $51.05   $51.00  
  Purchase #6 $93.74   12.626%   $105.5756   $105.58   $105.60   $105.60  
  Purchase #7 $93.72   13.869%   $106.718   $106.72   $106.70   $106.70  
  7 purchase totals = $951.88       $1,007.7224   $1,007.74   $1,007.75   $1,007.70