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 $247.99   4.564%   $259.3083   $259.31   $259.30   $259.30  
  Purchase #2 $68.63   4.420%   $71.6634   $71.66   $71.65   $71.70  
  Purchase #3 $81.84   7.544%   $88.014   $88.01   $88.00   $88.00  
  Purchase #4 $204.42   7.202%   $219.1423   $219.14   $219.15   $219.10  
  Purchase #5 $164.81   13.173%   $186.5204   $186.52   $186.50   $186.50  
  Purchase #6 $236.25   7.238%   $253.3498   $253.35   $253.35   $253.30  
  Purchase #7 $122.42   8.407%   $132.7118   $132.71   $132.70   $132.70  
  7 purchase totals = $1,126.36       $1,210.7100   $1,210.70   $1,210.65   $1,210.60