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 $55.84   10.278%   $61.5792   $61.58   $61.60   $61.60  
  Purchase #2 $199.38   7.382%   $214.0982   $214.10   $214.10   $214.10  
  Purchase #3 $23.53   13.189%   $26.6334   $26.63   $26.65   $26.60  
  Purchase #4 $147.40   12.587%   $165.9532   $165.95   $165.95   $166.00  
  Purchase #5 $226.50   10.872%   $251.1251   $251.13   $251.15   $251.10  
  Purchase #6 $177.81   13.294%   $201.4481   $201.45   $201.45   $201.40  
  Purchase #7 $144.59   8.109%   $156.3148   $156.31   $156.30   $156.30  
  7 purchase totals = $975.05       $1,077.1520   $1,077.15   $1,077.20   $1,077.10