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 $23.71   10.372%   $26.1692   $26.17   $26.15   $26.20  
  Purchase #2 $86.29   8.613%   $93.7222   $93.72   $93.70   $93.70  
  Purchase #3 $247.61   13.704%   $281.5425   $281.54   $281.55   $281.50  
  Purchase #4 $223.88   12.143%   $251.0657   $251.07   $251.05   $251.10  
  Purchase #5 $54.81   6.672%   $58.4669   $58.47   $58.45   $58.50  
  Purchase #6 $161.81   13.190%   $183.1527   $183.15   $183.15   $183.20  
  Purchase #7 $194.78   8.761%   $211.8447   $211.84   $211.85   $211.80  
  7 purchase totals = $992.89       $1,105.9639   $1,105.96   $1,105.90   $1,106.00