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 $33.74   8.582%   $36.6356   $36.64   $36.65   $36.60  
  Purchase #2 $58.89   10.453%   $65.0458   $65.05   $65.05   $65.00  
  Purchase #3 $247.94   13.325%   $280.978   $280.98   $281.00   $281.00  
  Purchase #4 $178.31   10.234%   $196.5582   $196.56   $196.55   $196.60  
  Purchase #5 $153.25   5.551%   $161.7569   $161.76   $161.75   $161.80  
  Purchase #6 $7.90   7.481%   $8.491   $8.49   $8.50   $8.50  
  Purchase #7 $163.27   5.159%   $171.6931   $171.69   $171.70   $171.70  
  7 purchase totals = $843.30       $921.1586   $921.17   $921.20   $921.20