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 $59.72   3.206%   $61.6346   $61.63   $61.65   $61.60  
  Purchase #2 $37.42   3.737%   $38.8184   $38.82   $38.80   $38.80  
  Purchase #3 $116.66   3.336%   $120.5518   $120.55   $120.55   $120.60  
  Purchase #4 $198.65   8.528%   $215.5909   $215.59   $215.60   $215.60  
  Purchase #5 $78.34   7.368%   $84.1121   $84.11   $84.10   $84.10  
  Purchase #6 $194.69   8.343%   $210.933   $210.93   $210.95   $210.90  
  Purchase #7 $225.28   4.311%   $234.9918   $234.99   $235.00   $235.00  
  7 purchase totals = $910.76       $966.6326   $966.62   $966.65   $966.60