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 $92.46   6.857%   $98.8   $98.80   $98.80   $98.80  
  Purchase #2 $70.49   9.589%   $77.2493   $77.25   $77.25   $77.20  
  Purchase #3 $54.68   8.389%   $59.2671   $59.27   $59.25   $59.30  
  Purchase #4 $185.33   6.595%   $197.5525   $197.55   $197.55   $197.60  
  Purchase #5 $167.65   7.187%   $179.699   $179.70   $179.70   $179.70  
  Purchase #6 $38.36   7.142%   $41.0997   $41.10   $41.10   $41.10  
  Purchase #7 $24.28   6.594%   $25.881   $25.88   $25.90   $25.90  
  7 purchase totals = $633.25       $679.5486   $679.55   $679.55   $679.60