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 $114.89   10.131%   $126.5295   $126.53   $126.55   $126.50  
  Purchase #2 $87.84   6.626%   $93.6603   $93.66   $93.65   $93.70  
  Purchase #3 $45.55   4.816%   $47.7437   $47.74   $47.75   $47.70  
  Purchase #4 $159.62   12.229%   $179.1399   $179.14   $179.15   $179.10  
  Purchase #5 $243.98   7.396%   $262.0248   $262.02   $262.00   $262.00  
  Purchase #6 $92.64   7.830%   $99.8937   $99.89   $99.90   $99.90  
  Purchase #7 $210.67   13.824%   $239.793   $239.79   $239.80   $239.80  
  7 purchase totals = $955.19       $1,048.7849   $1,048.77   $1,048.80   $1,048.70