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 $249.31   4.822%   $261.3317   $261.33   $261.35   $261.30  
  Purchase #2 $118.92   4.407%   $124.1608   $124.16   $124.15   $124.20  
  Purchase #3 $38.44   10.688%   $42.5485   $42.55   $42.55   $42.50  
  Purchase #4 $200.67   12.164%   $225.0795   $225.08   $225.10   $225.10  
  Purchase #5 $126.33   11.490%   $140.8453   $140.85   $140.85   $140.80  
  Purchase #6 $203.74   5.839%   $215.6364   $215.64   $215.65   $215.60  
  Purchase #7 $241.54   4.411%   $252.1943   $252.19   $252.20   $252.20  
  7 purchase totals = $1,178.95       $1,261.7965   $1,261.80   $1,261.85   $1,261.70