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 $118.58   10.787%   $131.3712   $131.37   $131.35   $131.40  
  Purchase #2 $224.64   3.508%   $232.5204   $232.52   $232.50   $232.50  
  Purchase #3 $191.63   5.719%   $202.5893   $202.59   $202.60   $202.60  
  Purchase #4 $39.89   11.444%   $44.455   $44.46   $44.45   $44.50  
  Purchase #5 $174.28   6.674%   $185.9114   $185.91   $185.90   $185.90  
  Purchase #6 $250.39   13.757%   $284.8362   $284.84   $284.85   $284.80  
  Purchase #7 $116.92   6.769%   $124.8343   $124.83   $124.85   $124.80  
  7 purchase totals = $1,116.33       $1,206.5178   $1,206.52   $1,206.50   $1,206.50