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 $17.46   11.228%   $19.4204   $19.42   $19.40   $19.40  
  Purchase #2 $220.89   3.410%   $228.4223   $228.42   $228.40   $228.40  
  Purchase #3 $46.93   5.857%   $49.6787   $49.68   $49.70   $49.70  
  Purchase #4 $181.76   3.669%   $188.4288   $188.43   $188.45   $188.40  
  Purchase #5 $204.80   12.187%   $229.759   $229.76   $229.75   $229.80  
  Purchase #6 $130.69   13.115%   $147.83   $147.83   $147.85   $147.80  
  Purchase #7 $164.93   3.759%   $171.1297   $171.13   $171.15   $171.10  
  7 purchase totals = $967.46       $1,034.6689   $1,034.67   $1,034.70   $1,034.60