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 $236.68   12.106%   $265.3325   $265.33   $265.35   $265.30  
  Purchase #2 $208.38   11.646%   $232.6479   $232.65   $232.65   $232.60  
  Purchase #3 $10.32   8.308%   $11.1774   $11.18   $11.20   $11.20  
  Purchase #4 $5.83   5.740%   $6.1646   $6.16   $6.15   $6.20  
  Purchase #5 $90.48   3.182%   $93.3591   $93.36   $93.35   $93.40  
  Purchase #6 $203.71   3.431%   $210.6993   $210.70   $210.70   $210.70  
  Purchase #7 $228.80   6.340%   $243.3059   $243.31   $243.30   $243.30  
  7 purchase totals = $984.20       $1,062.6867   $1,062.69   $1,062.70   $1,062.70