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 $216.83   9.598%   $237.6413   $237.64   $237.65   $237.60  
  Purchase #2 $235.70   13.411%   $267.3097   $267.31   $267.30   $267.30  
  Purchase #3 $80.78   10.728%   $89.4461   $89.45   $89.45   $89.40  
  Purchase #4 $24.90   8.144%   $26.9279   $26.93   $26.95   $26.90  
  Purchase #5 $68.33   13.790%   $77.7527   $77.75   $77.75   $77.80  
  Purchase #6 $116.47   5.171%   $122.4927   $122.49   $122.50   $122.50  
  Purchase #7 $146.61   9.824%   $161.013   $161.01   $161.00   $161.00  
  7 purchase totals = $889.62       $982.5834   $982.58   $982.60   $982.50