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 $166.94   9.127%   $182.1766   $182.18   $182.20   $182.20  
  Purchase #2 $106.65   12.230%   $119.6933   $119.69   $119.70   $119.70  
  Purchase #3 $214.74   9.629%   $235.4173   $235.42   $235.40   $235.40  
  Purchase #4 $47.94   3.677%   $49.7028   $49.70   $49.70   $49.70  
  Purchase #5 $215.81   11.800%   $241.2756   $241.28   $241.30   $241.30  
  Purchase #6 $196.47   6.685%   $209.604   $209.60   $209.60   $209.60  
  Purchase #7 $148.45   11.291%   $165.2115   $165.21   $165.20   $165.20  
  7 purchase totals = $1,097.00       $1,203.0811   $1,203.08   $1,203.10   $1,203.10