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 $161.96   11.755%   $180.9984   $181.00   $181.00   $181.00  
  Purchase #2 $234.49   12.106%   $262.8774   $262.88   $262.90   $262.90  
  Purchase #3 $65.70   9.241%   $71.7713   $71.77   $71.75   $71.80  
  Purchase #4 $174.46   4.679%   $182.623   $182.62   $182.60   $182.60  
  Purchase #5 $64.95   4.719%   $68.015   $68.02   $68.00   $68.00  
  Purchase #6 $58.31   4.224%   $60.773   $60.77   $60.75   $60.80  
  Purchase #7 $72.37   8.241%   $78.334   $78.33   $78.35   $78.30  
  7 purchase totals = $832.24       $905.3921   $905.39   $905.35   $905.40