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 $234.32   5.463%   $247.1209   $247.12   $247.10   $247.10  
  Purchase #2 $61.33   12.473%   $68.9797   $68.98   $69.00   $69.00  
  Purchase #3 $208.58   13.525%   $236.7904   $236.79   $236.80   $236.80  
  Purchase #4 $239.93   5.407%   $252.903   $252.90   $252.90   $252.90  
  Purchase #5 $24.92   5.245%   $26.2271   $26.23   $26.25   $26.20  
  Purchase #6 $222.31   3.617%   $230.351   $230.35   $230.35   $230.40  
  Purchase #7 $81.67   4.135%   $85.0471   $85.05   $85.05   $85.00  
  7 purchase totals = $1,073.06       $1,147.4192   $1,147.42   $1,147.45   $1,147.40