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 $191.55   10.690%   $212.0267   $212.03   $212.05   $212.00  
  Purchase #2 $185.85   8.137%   $200.9726   $200.97   $200.95   $201.00  
  Purchase #3 $16.74   6.183%   $17.775   $17.78   $17.80   $17.80  
  Purchase #4 $159.30   3.470%   $164.8277   $164.83   $164.85   $164.80  
  Purchase #5 $81.36   6.874%   $86.9527   $86.95   $86.95   $87.00  
  Purchase #6 $96.60   7.650%   $103.9899   $103.99   $104.00   $104.00  
  Purchase #7 $160.40   13.102%   $181.4156   $181.42   $181.40   $181.40  
  7 purchase totals = $891.80       $967.9602   $967.97   $968.00   $968.00