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 $62.25   10.365%   $68.7022   $68.70   $68.70   $68.70  
  Purchase #2 $90.43   11.320%   $100.6667   $100.67   $100.65   $100.70  
  Purchase #3 $151.92   8.745%   $165.2054   $165.21   $165.20   $165.20  
  Purchase #4 $224.38   9.286%   $245.2159   $245.22   $245.20   $245.20  
  Purchase #5 $237.48   5.715%   $251.052   $251.05   $251.05   $251.10  
  Purchase #6 $70.75   3.482%   $73.2135   $73.21   $73.20   $73.20  
  Purchase #7 $249.44   9.542%   $273.2416   $273.24   $273.25   $273.20  
  7 purchase totals = $1,086.65       $1,177.2973   $1,177.30   $1,177.25   $1,177.30