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 $227.46   10.327%   $250.9498   $250.95   $250.95   $250.90  
  Purchase #2 $56.75   7.489%   $61   $61.00   $61.00   $61.00  
  Purchase #3 $148.41   4.624%   $155.2725   $155.27   $155.25   $155.30  
  Purchase #4 $188.26   10.309%   $207.6677   $207.67   $207.65   $207.70  
  Purchase #5 $67.75   11.382%   $75.4613   $75.46   $75.45   $75.50  
  Purchase #6 $187.85   13.557%   $213.3168   $213.32   $213.30   $213.30  
  Purchase #7 $39.58   9.458%   $43.3235   $43.32   $43.30   $43.30  
  7 purchase totals = $916.06       $1,006.9916   $1,006.99   $1,006.90   $1,007.00