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 $233.77   12.360%   $262.664   $262.66   $262.65   $262.70  
  Purchase #2 $33.76   9.333%   $36.9108   $36.91   $36.90   $36.90  
  Purchase #3 $116.85   11.661%   $130.4759   $130.48   $130.50   $130.50  
  Purchase #4 $190.57   7.648%   $205.1448   $205.14   $205.15   $205.10  
  Purchase #5 $23.33   5.132%   $24.5273   $24.53   $24.55   $24.50  
  Purchase #6 $208.89   12.841%   $235.7136   $235.71   $235.70   $235.70  
  Purchase #7 $120.29   5.756%   $127.2139   $127.21   $127.20   $127.20  
  7 purchase totals = $927.46       $1,022.6503   $1,022.64   $1,022.65   $1,022.60