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 $206.68   12.646%   $232.8168   $232.82   $232.80   $232.80  
  Purchase #2 $196.94   4.502%   $205.8062   $205.81   $205.80   $205.80  
  Purchase #3 $232.90   4.206%   $242.6958   $242.70   $242.70   $242.70  
  Purchase #4 $26.28   7.295%   $28.1971   $28.20   $28.20   $28.20  
  Purchase #5 $23.91   3.128%   $24.6579   $24.66   $24.65   $24.70  
  Purchase #6 $192.70   13.521%   $218.755   $218.76   $218.75   $218.80  
  Purchase #7 $59.80   3.454%   $61.8655   $61.87   $61.85   $61.90  
  7 purchase totals = $939.21       $1,014.7943   $1,014.82   $1,014.75   $1,014.90