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 $206.44   13.826%   $234.9824   $234.98   $235.00   $235.00  
  Purchase #2 $80.70   4.761%   $84.5421   $84.54   $84.55   $84.50  
  Purchase #3 $119.29   13.220%   $135.0601   $135.06   $135.05   $135.10  
  Purchase #4 $25.75   4.514%   $26.9124   $26.91   $26.90   $26.90  
  Purchase #5 $57.58   11.559%   $64.2357   $64.24   $64.25   $64.20  
  Purchase #6 $206.81   7.387%   $222.0871   $222.09   $222.10   $222.10  
  Purchase #7 $225.85   7.630%   $243.0824   $243.08   $243.10   $243.10  
  7 purchase totals = $922.42       $1,010.9022   $1,010.90   $1,010.95   $1,010.90