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 $58.48   12.239%   $65.6374   $65.64   $65.65   $65.60  
  Purchase #2 $120.80   6.339%   $128.4575   $128.46   $128.45   $128.50  
  Purchase #3 $164.38   11.486%   $183.2607   $183.26   $183.25   $183.30  
  Purchase #4 $204.25   6.211%   $216.936   $216.94   $216.95   $216.90  
  Purchase #5 $186.37   5.452%   $196.5309   $196.53   $196.55   $196.50  
  Purchase #6 $53.26   6.651%   $56.8023   $56.80   $56.80   $56.80  
  Purchase #7 $171.91   9.239%   $187.7928   $187.79   $187.80   $187.80  
  7 purchase totals = $959.45       $1,035.4176   $1,035.42   $1,035.45   $1,035.40