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 $56.40   9.335%   $61.6649   $61.66   $61.65   $61.70  
  Purchase #2 $207.85   10.868%   $230.4391   $230.44   $230.45   $230.40  
  Purchase #3 $154.54   13.589%   $175.5404   $175.54   $175.55   $175.50  
  Purchase #4 $35.68   3.456%   $36.9131   $36.91   $36.90   $36.90  
  Purchase #5 $125.36   9.140%   $136.8179   $136.82   $136.80   $136.80  
  Purchase #6 $179.68   7.105%   $192.4463   $192.45   $192.45   $192.40  
  Purchase #7 $165.55   9.346%   $181.0223   $181.02   $181.00   $181.00  
  7 purchase totals = $925.06       $1,014.8440   $1,014.84   $1,014.80   $1,014.70