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 $76.99   13.874%   $87.6716   $87.67   $87.65   $87.70  
  Purchase #2 $63.33   4.364%   $66.0937   $66.09   $66.10   $66.10  
  Purchase #3 $152.44   5.597%   $160.9721   $160.97   $160.95   $161.00  
  Purchase #4 $112.32   12.455%   $126.3095   $126.31   $126.30   $126.30  
  Purchase #5 $228.63   4.835%   $239.6843   $239.68   $239.70   $239.70  
  Purchase #6 $207.32   13.833%   $235.9986   $236.00   $236.00   $236.00  
  Purchase #7 $181.36   4.220%   $189.0134   $189.01   $189.00   $189.00  
  7 purchase totals = $1,022.39       $1,105.7432   $1,105.73   $1,105.70   $1,105.80