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 $23.98   8.243%   $25.9567   $25.96   $25.95   $26.00  
  Purchase #2 $59.58   11.466%   $66.4114   $66.41   $66.40   $66.40  
  Purchase #3 $195.25   12.521%   $219.6973   $219.70   $219.70   $219.70  
  Purchase #4 $195.80   11.383%   $218.0879   $218.09   $218.10   $218.10  
  Purchase #5 $245.75   8.159%   $265.8007   $265.80   $265.80   $265.80  
  Purchase #6 $205.76   10.643%   $227.659   $227.66   $227.65   $227.70  
  Purchase #7 $29.90   7.284%   $32.0779   $32.08   $32.10   $32.10  
  7 purchase totals = $956.02       $1,055.6909   $1,055.70   $1,055.70   $1,055.80