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 $59.86   3.641%   $62.0395   $62.04   $62.05   $62.00  
  Purchase #2 $248.32   11.527%   $276.9438   $276.94   $276.95   $276.90  
  Purchase #3 $134.90   10.337%   $148.8446   $148.84   $148.85   $148.80  
  Purchase #4 $56.45   9.508%   $61.8173   $61.82   $61.80   $61.80  
  Purchase #5 $237.69   7.346%   $255.1507   $255.15   $255.15   $255.20  
  Purchase #6 $237.99   3.458%   $246.2197   $246.22   $246.20   $246.20  
  Purchase #7 $172.36   9.640%   $188.9755   $188.98   $189.00   $189.00  
  7 purchase totals = $1,147.57       $1,239.9911   $1,239.99   $1,240.00   $1,239.90