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 $218.54   10.759%   $242.0527   $242.05   $242.05   $242.10  
  Purchase #2 $148.91   9.445%   $162.9745   $162.97   $162.95   $163.00  
  Purchase #3 $68.73   3.373%   $71.0483   $71.05   $71.05   $71.00  
  Purchase #4 $27.33   5.443%   $28.8176   $28.82   $28.80   $28.80  
  Purchase #5 $40.32   9.102%   $43.9899   $43.99   $44.00   $44.00  
  Purchase #6 $218.95   3.490%   $226.5914   $226.59   $226.60   $226.60  
  Purchase #7 $174.85   3.344%   $180.697   $180.70   $180.70   $180.70  
  7 purchase totals = $897.63       $956.1714   $956.17   $956.15   $956.20