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 $112.93   12.292%   $126.8114   $126.81   $126.80   $126.80  
  Purchase #2 $231.61   10.535%   $256.0101   $256.01   $256.00   $256.00  
  Purchase #3 $111.48   3.215%   $115.0641   $115.06   $115.05   $115.10  
  Purchase #4 $181.66   5.662%   $191.9456   $191.95   $191.95   $191.90  
  Purchase #5 $189.70   10.385%   $209.4003   $209.40   $209.40   $209.40  
  Purchase #6 $202.83   3.156%   $209.2313   $209.23   $209.25   $209.20  
  Purchase #7 $43.47   12.261%   $48.7999   $48.80   $48.80   $48.80  
  7 purchase totals = $1,073.68       $1,157.2627   $1,157.26   $1,157.25   $1,157.20