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 $55.77   10.197%   $61.4569   $61.46   $61.45   $61.50  
  Purchase #2 $94.89   7.181%   $101.7041   $101.70   $101.70   $101.70  
  Purchase #3 $18.58   11.440%   $20.7056   $20.71   $20.70   $20.70  
  Purchase #4 $169.58   11.165%   $188.5136   $188.51   $188.50   $188.50  
  Purchase #5 $187.69   8.456%   $203.5611   $203.56   $203.55   $203.60  
  Purchase #6 $173.51   7.357%   $186.2751   $186.28   $186.30   $186.30  
  Purchase #7 $165.51   6.480%   $176.235   $176.24   $176.25   $176.20  
  7 purchase totals = $865.53       $938.4514   $938.46   $938.45   $938.50