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 $60.91   13.807%   $69.3198   $69.32   $69.30   $69.30  
  Purchase #2 $208.32   11.269%   $231.7956   $231.80   $231.80   $231.80  
  Purchase #3 $165.49   4.463%   $172.8758   $172.88   $172.90   $172.90  
  Purchase #4 $222.67   13.414%   $252.539   $252.54   $252.55   $252.50  
  Purchase #5 $134.37   12.730%   $151.4753   $151.48   $151.50   $151.50  
  Purchase #6 $208.73   7.688%   $224.7772   $224.78   $224.80   $224.80  
  Purchase #7 $55.53   3.109%   $57.2564   $57.26   $57.25   $57.30  
  7 purchase totals = $1,056.02       $1,160.0391   $1,160.06   $1,160.10   $1,160.10