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 $98.70   8.464%   $107.054   $107.05   $107.05   $107.10  
  Purchase #2 $81.76   12.712%   $92.1533   $92.15   $92.15   $92.20  
  Purchase #3 $154.40   13.846%   $175.7782   $175.78   $175.80   $175.80  
  Purchase #4 $163.39   9.649%   $179.1555   $179.16   $179.15   $179.20  
  Purchase #5 $69.82   11.252%   $77.6761   $77.68   $77.70   $77.70  
  Purchase #6 $187.74   6.854%   $200.6077   $200.61   $200.60   $200.60  
  Purchase #7 $234.78   5.124%   $246.8101   $246.81   $246.80   $246.80  
  7 purchase totals = $990.59       $1,079.2349   $1,079.24   $1,079.25   $1,079.40