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 $207.98   7.747%   $224.0922   $224.09   $224.10   $224.10  
  Purchase #2 $152.42   6.455%   $162.2587   $162.26   $162.25   $162.30  
  Purchase #3 $23.83   3.847%   $24.7467   $24.75   $24.75   $24.70  
  Purchase #4 $107.93   10.218%   $118.9583   $118.96   $118.95   $119.00  
  Purchase #5 $67.82   9.130%   $74.012   $74.01   $74.00   $74.00  
  Purchase #6 $200.97   7.328%   $215.6971   $215.70   $215.70   $215.70  
  Purchase #7 $93.59   12.221%   $105.0276   $105.03   $105.05   $105.00  
  7 purchase totals = $854.54       $924.7926   $924.80   $924.80   $924.80