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 $218.58   7.793%   $235.6139   $235.61   $235.60   $235.60  
  Purchase #2 $37.64   12.267%   $42.2573   $42.26   $42.25   $42.30  
  Purchase #3 $208.82   10.520%   $230.7879   $230.79   $230.80   $230.80  
  Purchase #4 $119.32   3.281%   $123.2349   $123.23   $123.25   $123.20  
  Purchase #5 $106.71   13.326%   $120.9302   $120.93   $120.95   $120.90  
  Purchase #6 $216.86   10.823%   $240.3308   $240.33   $240.35   $240.30  
  Purchase #7 $19.36   8.239%   $20.9551   $20.96   $20.95   $21.00  
  7 purchase totals = $927.29       $1,014.1101   $1,014.11   $1,014.15   $1,014.10