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 $202.51   11.228%   $225.2478   $225.25   $225.25   $225.20  
  Purchase #2 $91.41   10.708%   $101.1982   $101.20   $101.20   $101.20  
  Purchase #3 $191.56   7.702%   $206.314   $206.31   $206.30   $206.30  
  Purchase #4 $130.74   9.706%   $143.4296   $143.43   $143.45   $143.40  
  Purchase #5 $61.51   12.162%   $68.9908   $68.99   $69.00   $69.00  
  Purchase #6 $187.88   5.665%   $198.5234   $198.52   $198.50   $198.50  
  Purchase #7 $72.63   13.402%   $82.3639   $82.36   $82.35   $82.40  
  7 purchase totals = $938.24       $1,026.0677   $1,026.06   $1,026.05   $1,026.00