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 $223.41   10.545%   $246.9686   $246.97   $246.95   $247.00  
  Purchase #2 $169.72   6.782%   $181.2304   $181.23   $181.25   $181.20  
  Purchase #3 $44.30   9.334%   $48.435   $48.44   $48.45   $48.40  
  Purchase #4 $168.80   5.163%   $177.5151   $177.52   $177.50   $177.50  
  Purchase #5 $140.40   11.443%   $156.466   $156.47   $156.45   $156.50  
  Purchase #6 $14.63   13.267%   $16.571   $16.57   $16.55   $16.60  
  Purchase #7 $73.34   11.260%   $81.5981   $81.60   $81.60   $81.60  
  7 purchase totals = $834.60       $908.7842   $908.80   $908.75   $908.80