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 $188.35   9.298%   $205.8628   $205.86   $205.85   $205.90  
  Purchase #2 $184.77   5.383%   $194.7162   $194.72   $194.70   $194.70  
  Purchase #3 $152.52   8.543%   $165.5498   $165.55   $165.55   $165.50  
  Purchase #4 $137.58   13.330%   $155.9194   $155.92   $155.90   $155.90  
  Purchase #5 $195.56   10.289%   $215.6812   $215.68   $215.70   $215.70  
  Purchase #6 $163.38   8.563%   $177.3702   $177.37   $177.35   $177.40  
  Purchase #7 $114.87   10.405%   $126.8222   $126.82   $126.80   $126.80  
  7 purchase totals = $1,137.03       $1,241.9218   $1,241.92   $1,241.85   $1,241.90