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 $53.76   8.331%   $58.2387   $58.24   $58.25   $58.20  
  Purchase #2 $226.28   10.792%   $250.7001   $250.70   $250.70   $250.70  
  Purchase #3 $130.30   10.814%   $144.3906   $144.39   $144.40   $144.40  
  Purchase #4 $183.86   5.450%   $193.8804   $193.88   $193.90   $193.90  
  Purchase #5 $216.64   7.666%   $233.2476   $233.25   $233.25   $233.20  
  Purchase #6 $250.29   5.603%   $264.3137   $264.31   $264.30   $264.30  
  Purchase #7 $226.49   12.424%   $254.6291   $254.63   $254.65   $254.60  
  7 purchase totals = $1,287.62       $1,399.4002   $1,399.40   $1,399.45   $1,399.30