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 $236.60   13.200%   $267.8312   $267.83   $267.85   $267.80  
  Purchase #2 $165.41   10.176%   $182.2421   $182.24   $182.25   $182.20  
  Purchase #3 $229.45   4.258%   $239.22   $239.22   $239.20   $239.20  
  Purchase #4 $45.93   3.740%   $47.6478   $47.65   $47.65   $47.60  
  Purchase #5 $243.34   9.547%   $266.5717   $266.57   $266.55   $266.60  
  Purchase #6 $185.35   3.642%   $192.1004   $192.10   $192.10   $192.10  
  Purchase #7 $121.84   10.870%   $135.084   $135.08   $135.10   $135.10  
  7 purchase totals = $1,227.92       $1,330.6972   $1,330.69   $1,330.70   $1,330.60