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 $26.80   11.670%   $29.9276   $29.93   $29.95   $29.90  
  Purchase #2 $73.71   11.167%   $81.9412   $81.94   $81.95   $81.90  
  Purchase #3 $139.29   10.796%   $154.3277   $154.33   $154.35   $154.30  
  Purchase #4 $210.36   10.373%   $232.1806   $232.18   $232.20   $232.20  
  Purchase #5 $197.53   13.437%   $224.0721   $224.07   $224.05   $224.10  
  Purchase #6 $195.66   3.681%   $202.8622   $202.86   $202.85   $202.90  
  Purchase #7 $80.36   7.826%   $86.649   $86.65   $86.65   $86.60  
  7 purchase totals = $923.71       $1,011.9604   $1,011.96   $1,012.00   $1,011.90