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 $196.31   4.629%   $205.3972   $205.40   $205.40   $205.40  
  Purchase #2 $126.91   13.661%   $144.2472   $144.25   $144.25   $144.20  
  Purchase #3 $45.93   8.355%   $49.7675   $49.77   $49.75   $49.80  
  Purchase #4 $232.36   6.506%   $247.4773   $247.48   $247.50   $247.50  
  Purchase #5 $9.52   11.753%   $10.6389   $10.64   $10.65   $10.60  
  Purchase #6 $141.29   13.288%   $160.0646   $160.06   $160.05   $160.10  
  Purchase #7 $162.73   8.286%   $176.2138   $176.21   $176.20   $176.20  
  7 purchase totals = $915.05       $993.8065   $993.81   $993.80   $993.80