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 $214.88   9.323%   $234.9133   $234.91   $234.90   $234.90  
  Purchase #2 $118.57   12.811%   $133.76   $133.76   $133.75   $133.80  
  Purchase #3 $81.29   5.121%   $85.4529   $85.45   $85.45   $85.50  
  Purchase #4 $167.43   6.563%   $178.4184   $178.42   $178.40   $178.40  
  Purchase #5 $26.84   6.776%   $28.6587   $28.66   $28.65   $28.70  
  Purchase #6 $120.69   7.795%   $130.0978   $130.10   $130.10   $130.10  
  Purchase #7 $166.84   8.691%   $181.3401   $181.34   $181.35   $181.30  
  7 purchase totals = $896.54       $972.6412   $972.64   $972.60   $972.70