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 $183.91   9.318%   $201.0467   $201.05   $201.05   $201.00  
  Purchase #2 $35.36   4.666%   $37.0099   $37.01   $37.00   $37.00  
  Purchase #3 $235.33   6.740%   $251.1912   $251.19   $251.20   $251.20  
  Purchase #4 $24.46   9.604%   $26.8091   $26.81   $26.80   $26.80  
  Purchase #5 $43.78   9.691%   $48.0227   $48.02   $48.00   $48.00  
  Purchase #6 $136.66   13.133%   $154.6076   $154.61   $154.60   $154.60  
  Purchase #7 $174.34   4.360%   $181.9412   $181.94   $181.95   $181.90  
  7 purchase totals = $833.84       $900.6284   $900.63   $900.60   $900.50