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 $190.39   7.785%   $205.2119   $205.21   $205.20   $205.20  
  Purchase #2 $246.25   5.829%   $260.6039   $260.60   $260.60   $260.60  
  Purchase #3 $74.71   11.621%   $83.392   $83.39   $83.40   $83.40  
  Purchase #4 $226.49   4.270%   $236.1611   $236.16   $236.15   $236.20  
  Purchase #5 $136.90   11.563%   $152.7297   $152.73   $152.75   $152.70  
  Purchase #6 $186.43   3.767%   $193.4528   $193.45   $193.45   $193.50  
  Purchase #7 $66.94   8.623%   $72.7122   $72.71   $72.70   $72.70  
  7 purchase totals = $1,128.11       $1,204.2636   $1,204.25   $1,204.25   $1,204.30