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 $54.29   12.486%   $61.0686   $61.07   $61.05   $61.10  
  Purchase #2 $179.50   6.280%   $190.7726   $190.77   $190.75   $190.80  
  Purchase #3 $187.45   8.384%   $203.1658   $203.17   $203.15   $203.20  
  Purchase #4 $240.28   8.597%   $260.9369   $260.94   $260.95   $260.90  
  Purchase #5 $191.67   13.488%   $217.5224   $217.52   $217.50   $217.50  
  Purchase #6 $196.69   5.748%   $207.9957   $208.00   $208.00   $208.00  
  Purchase #7 $205.63   8.312%   $222.722   $222.72   $222.70   $222.70  
  7 purchase totals = $1,255.51       $1,364.1840   $1,364.19   $1,364.10   $1,364.20