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 $62.47   10.319%   $68.9163   $68.92   $68.90   $68.90  
  Purchase #2 $191.31   9.692%   $209.8518   $209.85   $209.85   $209.90  
  Purchase #3 $232.26   9.189%   $253.6024   $253.60   $253.60   $253.60  
  Purchase #4 $59.36   10.493%   $65.5886   $65.59   $65.60   $65.60  
  Purchase #5 $229.67   13.685%   $261.1003   $261.10   $261.10   $261.10  
  Purchase #6 $154.76   12.220%   $173.6717   $173.67   $173.65   $173.70  
  Purchase #7 $245.36   12.573%   $276.2091   $276.21   $276.20   $276.20  
  7 purchase totals = $1,175.19       $1,308.9402   $1,308.94   $1,308.90   $1,309.00