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 $210.85   8.436%   $228.6373   $228.64   $228.65   $228.60  
  Purchase #2 $71.77   12.349%   $80.6329   $80.63   $80.65   $80.60  
  Purchase #3 $22.99   4.491%   $24.0225   $24.02   $24.00   $24.00  
  Purchase #4 $116.66   8.139%   $126.155   $126.16   $126.15   $126.20  
  Purchase #5 $240.84   12.787%   $271.6362   $271.64   $271.65   $271.60  
  Purchase #6 $68.67   12.304%   $77.1192   $77.12   $77.10   $77.10  
  Purchase #7 $237.72   5.106%   $249.858   $249.86   $249.85   $249.90  
  7 purchase totals = $969.50       $1,058.0611   $1,058.07   $1,058.05   $1,058.00