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 $187.58   13.862%   $213.5823   $213.58   $213.60   $213.60  
  Purchase #2 $153.86   8.607%   $167.1027   $167.10   $167.10   $167.10  
  Purchase #3 $71.91   8.558%   $78.0641   $78.06   $78.05   $78.10  
  Purchase #4 $245.38   6.309%   $260.861   $260.86   $260.85   $260.90  
  Purchase #5 $83.45   3.301%   $86.2047   $86.20   $86.20   $86.20  
  Purchase #6 $83.26   4.771%   $87.2323   $87.23   $87.25   $87.20  
  Purchase #7 $141.93   11.815%   $158.699   $158.70   $158.70   $158.70  
  7 purchase totals = $967.37       $1,051.7461   $1,051.73   $1,051.75   $1,051.80