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 $44.33   6.756%   $47.3249   $47.32   $47.30   $47.30  
  Purchase #2 $160.49   13.551%   $182.238   $182.24   $182.25   $182.20  
  Purchase #3 $45.50   11.839%   $50.8867   $50.89   $50.90   $50.90  
  Purchase #4 $25.41   12.721%   $28.6424   $28.64   $28.65   $28.60  
  Purchase #5 $166.35   5.523%   $175.5375   $175.54   $175.55   $175.50  
  Purchase #6 $207.76   7.338%   $223.0054   $223.01   $223.00   $223.00  
  Purchase #7 $221.75   6.663%   $236.5252   $236.53   $236.55   $236.50  
  7 purchase totals = $871.59       $944.1601   $944.17   $944.20   $944.00