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 $22.84   8.102%   $24.6905   $24.69   $24.70   $24.70  
  Purchase #2 $183.99   3.709%   $190.8142   $190.81   $190.80   $190.80  
  Purchase #3 $213.46   5.197%   $224.5535   $224.55   $224.55   $224.60  
  Purchase #4 $236.51   5.765%   $250.1448   $250.14   $250.15   $250.10  
  Purchase #5 $191.57   6.855%   $204.7021   $204.70   $204.70   $204.70  
  Purchase #6 $99.54   6.668%   $106.1773   $106.18   $106.20   $106.20  
  Purchase #7 $243.61   6.314%   $258.9915   $258.99   $259.00   $259.00  
  7 purchase totals = $1,191.52       $1,260.0739   $1,260.06   $1,260.10   $1,260.10