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 $14.94   10.713%   $16.5405   $16.54   $16.55   $16.50  
  Purchase #2 $135.42   11.666%   $151.2181   $151.22   $151.20   $151.20  
  Purchase #3 $69.36   10.135%   $76.3896   $76.39   $76.40   $76.40  
  Purchase #4 $151.59   8.857%   $165.0163   $165.02   $165.00   $165.00  
  Purchase #5 $212.39   5.226%   $223.4895   $223.49   $223.50   $223.50  
  Purchase #6 $222.40   8.268%   $240.788   $240.79   $240.80   $240.80  
  Purchase #7 $227.30   6.715%   $242.5632   $242.56   $242.55   $242.60  
  7 purchase totals = $1,033.40       $1,116.0052   $1,116.01   $1,116.00   $1,116.00