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 $116.81   11.846%   $130.6473   $130.65   $130.65   $130.60  
  Purchase #2 $82.57   13.443%   $93.6699   $93.67   $93.65   $93.70  
  Purchase #3 $122.55   12.839%   $138.2842   $138.28   $138.30   $138.30  
  Purchase #4 $204.60   10.744%   $226.5822   $226.58   $226.60   $226.60  
  Purchase #5 $179.28   4.690%   $187.6882   $187.69   $187.70   $187.70  
  Purchase #6 $116.49   7.849%   $125.6333   $125.63   $125.65   $125.60  
  Purchase #7 $114.80   13.654%   $130.4748   $130.47   $130.45   $130.50  
  7 purchase totals = $937.10       $1,032.9799   $1,032.97   $1,033.00   $1,033.00