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 $67.82   10.644%   $75.0388   $75.04   $75.05   $75.00  
  Purchase #2 $196.66   11.632%   $219.5355   $219.54   $219.55   $219.50  
  Purchase #3 $226.64   13.571%   $257.3973   $257.40   $257.40   $257.40  
  Purchase #4 $123.39   10.332%   $136.1387   $136.14   $136.15   $136.10  
  Purchase #5 $86.52   3.798%   $89.806   $89.81   $89.80   $89.80  
  Purchase #6 $79.63   10.189%   $87.7435   $87.74   $87.75   $87.70  
  Purchase #7 $206.49   5.825%   $218.518   $218.52   $218.50   $218.50  
  7 purchase totals = $987.15       $1,084.1778   $1,084.19   $1,084.20   $1,084.00