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 $54.33   3.227%   $56.0832   $56.08   $56.10   $56.10  
  Purchase #2 $192.34   7.803%   $207.3483   $207.35   $207.35   $207.30  
  Purchase #3 $222.75   11.419%   $248.1858   $248.19   $248.20   $248.20  
  Purchase #4 $127.39   7.386%   $136.799   $136.80   $136.80   $136.80  
  Purchase #5 $222.33   3.769%   $230.7096   $230.71   $230.70   $230.70  
  Purchase #6 $107.33   13.637%   $121.9666   $121.97   $121.95   $122.00  
  Purchase #7 $21.49   13.736%   $24.4419   $24.44   $24.45   $24.40  
  7 purchase totals = $947.96       $1,025.5344   $1,025.54   $1,025.55   $1,025.50