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 $241.57   11.183%   $268.5848   $268.58   $268.60   $268.60  
  Purchase #2 $147.70   11.852%   $165.2054   $165.21   $165.20   $165.20  
  Purchase #3 $142.60   5.196%   $150.0095   $150.01   $150.00   $150.00  
  Purchase #4 $196.36   7.695%   $211.4699   $211.47   $211.45   $211.50  
  Purchase #5 $185.53   7.117%   $198.7342   $198.73   $198.75   $198.70  
  Purchase #6 $154.66   7.486%   $166.2378   $166.24   $166.25   $166.20  
  Purchase #7 $128.89   10.605%   $142.5588   $142.56   $142.55   $142.60  
  7 purchase totals = $1,197.31       $1,302.8004   $1,302.80   $1,302.80   $1,302.80