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 $146.27   11.658%   $163.3222   $163.32   $163.30   $163.30  
  Purchase #2 $237.93   5.133%   $250.1429   $250.14   $250.15   $250.10  
  Purchase #3 $137.56   3.396%   $142.2315   $142.23   $142.25   $142.20  
  Purchase #4 $8.83   8.425%   $9.5739   $9.57   $9.55   $9.60  
  Purchase #5 $225.81   4.801%   $236.6511   $236.65   $236.65   $236.70  
  Purchase #6 $24.97   7.751%   $26.9054   $26.91   $26.90   $26.90  
  Purchase #7 $134.42   10.854%   $149.0099   $149.01   $149.00   $149.00  
  7 purchase totals = $915.79       $977.8369   $977.83   $977.80   $977.80