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 $231.85   13.327%   $262.7486   $262.75   $262.75   $262.70  
  Purchase #2 $176.79   6.792%   $188.7976   $188.80   $188.80   $188.80  
  Purchase #3 $21.50   13.292%   $24.3578   $24.36   $24.35   $24.40  
  Purchase #4 $37.44   9.549%   $41.0151   $41.02   $41.00   $41.00  
  Purchase #5 $223.94   7.698%   $241.1789   $241.18   $241.20   $241.20  
  Purchase #6 $151.94   13.276%   $172.1116   $172.11   $172.10   $172.10  
  Purchase #7 $46.79   12.637%   $52.7029   $52.70   $52.70   $52.70  
  7 purchase totals = $890.25       $982.9125   $982.92   $982.90   $982.90