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 $133.29   10.662%   $147.5014   $147.50   $147.50   $147.50  
  Purchase #2 $216.58   10.608%   $239.5548   $239.55   $239.55   $239.60  
  Purchase #3 $193.34   5.254%   $203.4981   $203.50   $203.50   $203.50  
  Purchase #4 $142.25   12.119%   $159.4893   $159.49   $159.50   $159.50  
  Purchase #5 $161.76   13.591%   $183.7448   $183.74   $183.75   $183.70  
  Purchase #6 $22.43   6.477%   $23.8828   $23.88   $23.90   $23.90  
  Purchase #7 $57.84   6.424%   $61.5556   $61.56   $61.55   $61.60  
  7 purchase totals = $927.49       $1,019.2268   $1,019.22   $1,019.25   $1,019.30