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 $201.61   11.504%   $224.8032   $224.80   $224.80   $224.80  
  Purchase #2 $121.74   9.389%   $133.1702   $133.17   $133.15   $133.20  
  Purchase #3 $227.77   11.499%   $253.9613   $253.96   $253.95   $254.00  
  Purchase #4 $73.46   11.225%   $81.7059   $81.71   $81.70   $81.70  
  Purchase #5 $94.51   9.248%   $103.2503   $103.25   $103.25   $103.30  
  Purchase #6 $65.85   13.520%   $74.7529   $74.75   $74.75   $74.80  
  Purchase #7 $246.49   9.481%   $269.8597   $269.86   $269.85   $269.90  
  7 purchase totals = $1,031.43       $1,141.5035   $1,141.50   $1,141.45   $1,141.70