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 $132.79   10.426%   $146.6347   $146.63   $146.65   $146.60  
  Purchase #2 $98.69   4.326%   $102.9593   $102.96   $102.95   $103.00  
  Purchase #3 $157.35   4.599%   $164.5865   $164.59   $164.60   $164.60  
  Purchase #4 $62.49   8.432%   $67.7592   $67.76   $67.75   $67.80  
  Purchase #5 $187.61   10.755%   $207.7875   $207.79   $207.80   $207.80  
  Purchase #6 $116.39   10.522%   $128.6366   $128.64   $128.65   $128.60  
  Purchase #7 $156.62   12.364%   $175.9845   $175.98   $176.00   $176.00  
  7 purchase totals = $911.94       $994.3483   $994.35   $994.40   $994.40