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 $54.77   5.298%   $57.6717   $57.67   $57.65   $57.70  
  Purchase #2 $95.48   6.226%   $101.4246   $101.42   $101.40   $101.40  
  Purchase #3 $189.25   5.552%   $199.7572   $199.76   $199.75   $199.80  
  Purchase #4 $227.28   6.504%   $242.0623   $242.06   $242.05   $242.10  
  Purchase #5 $222.33   5.283%   $234.0757   $234.08   $234.10   $234.10  
  Purchase #6 $55.97   8.331%   $60.6329   $60.63   $60.65   $60.60  
  Purchase #7 $238.55   11.258%   $265.406   $265.41   $265.40   $265.40  
  7 purchase totals = $1,083.63       $1,161.0304   $1,161.03   $1,161.00   $1,161.10