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 $43.79   5.158%   $46.0487   $46.05   $46.05   $46.00  
  Purchase #2 $250.96   4.811%   $263.0337   $263.03   $263.05   $263.00  
  Purchase #3 $98.76   12.719%   $111.3213   $111.32   $111.30   $111.30  
  Purchase #4 $26.75   7.173%   $28.6688   $28.67   $28.65   $28.70  
  Purchase #5 $224.25   11.176%   $249.3122   $249.31   $249.30   $249.30  
  Purchase #6 $175.45   11.813%   $196.1759   $196.18   $196.20   $196.20  
  Purchase #7 $23.49   13.469%   $26.6539   $26.65   $26.65   $26.70  
  7 purchase totals = $843.45       $921.2145   $921.21   $921.20   $921.20