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 $237.58   11.547%   $265.0134   $265.01   $265.00   $265.00  
  Purchase #2 $110.90   11.441%   $123.5881   $123.59   $123.60   $123.60  
  Purchase #3 $216.56   10.446%   $239.1819   $239.18   $239.20   $239.20  
  Purchase #4 $43.57   11.644%   $48.6433   $48.64   $48.65   $48.60  
  Purchase #5 $91.72   12.560%   $103.24   $103.24   $103.25   $103.20  
  Purchase #6 $232.74   12.348%   $261.4787   $261.48   $261.50   $261.50  
  Purchase #7 $203.44   11.314%   $226.4572   $226.46   $226.45   $226.50  
  7 purchase totals = $1,136.51       $1,267.6026   $1,267.60   $1,267.65   $1,267.60