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 $247.48   8.438%   $268.3624   $268.36   $268.35   $268.40  
  Purchase #2 $241.68   9.417%   $264.439   $264.44   $264.45   $264.40  
  Purchase #3 $46.62   13.820%   $53.0629   $53.06   $53.05   $53.10  
  Purchase #4 $197.67   8.295%   $214.0667   $214.07   $214.05   $214.10  
  Purchase #5 $250.85   7.703%   $270.173   $270.17   $270.15   $270.20  
  Purchase #6 $180.69   11.558%   $201.5742   $201.57   $201.55   $201.60  
  Purchase #7 $147.76   13.384%   $167.5362   $167.54   $167.55   $167.50  
  7 purchase totals = $1,312.75       $1,439.2144   $1,439.21   $1,439.15   $1,439.30