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 $164.95   10.166%   $181.7188   $181.72   $181.70   $181.70  
  Purchase #2 $239.87   5.773%   $253.7177   $253.72   $253.70   $253.70  
  Purchase #3 $143.28   3.614%   $148.4581   $148.46   $148.45   $148.50  
  Purchase #4 $158.28   10.728%   $175.2603   $175.26   $175.25   $175.30  
  Purchase #5 $245.35   9.459%   $268.5577   $268.56   $268.55   $268.60  
  Purchase #6 $216.91   8.835%   $236.074   $236.07   $236.05   $236.10  
  Purchase #7 $243.85   6.799%   $260.4294   $260.43   $260.45   $260.40  
  7 purchase totals = $1,412.49       $1,524.2160   $1,524.22   $1,524.15   $1,524.30