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 $214.76   12.677%   $241.9851   $241.99   $242.00   $242.00  
  Purchase #2 $87.57   6.506%   $93.2673   $93.27   $93.25   $93.30  
  Purchase #3 $112.27   7.498%   $120.688   $120.69   $120.70   $120.70  
  Purchase #4 $219.52   6.672%   $234.1664   $234.17   $234.15   $234.20  
  Purchase #5 $208.57   10.837%   $231.1727   $231.17   $231.15   $231.20  
  Purchase #6 $106.39   12.248%   $119.4206   $119.42   $119.40   $119.40  
  Purchase #7 $15.79   12.834%   $17.8165   $17.82   $17.80   $17.80  
  7 purchase totals = $964.87       $1,058.5166   $1,058.53   $1,058.45   $1,058.60