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 $24.31   7.578%   $26.1522   $26.15   $26.15   $26.20  
  Purchase #2 $66.69   6.699%   $71.1576   $71.16   $71.15   $71.20  
  Purchase #3 $49.50   11.543%   $55.2138   $55.21   $55.20   $55.20  
  Purchase #4 $249.51   6.657%   $266.1199   $266.12   $266.10   $266.10  
  Purchase #5 $168.36   7.108%   $180.327   $180.33   $180.35   $180.30  
  Purchase #6 $152.91   11.858%   $171.0421   $171.04   $171.05   $171.00  
  Purchase #7 $211.26   11.606%   $235.7788   $235.78   $235.80   $235.80  
  7 purchase totals = $922.54       $1,005.7914   $1,005.79   $1,005.80   $1,005.80