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 $122.75   9.823%   $134.8077   $134.81   $134.80   $134.80  
  Purchase #2 $234.91   13.817%   $267.3675   $267.37   $267.35   $267.40  
  Purchase #3 $167.66   6.107%   $177.899   $177.90   $177.90   $177.90  
  Purchase #4 $56.42   9.321%   $61.6789   $61.68   $61.70   $61.70  
  Purchase #5 $152.52   4.544%   $159.4505   $159.45   $159.45   $159.50  
  Purchase #6 $164.88   13.270%   $186.7596   $186.76   $186.75   $186.80  
  Purchase #7 $244.48   3.628%   $253.3497   $253.35   $253.35   $253.30  
  7 purchase totals = $1,143.62       $1,241.3129   $1,241.32   $1,241.30   $1,241.40