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 $228.96   8.447%   $248.3003   $248.30   $248.30   $248.30  
  Purchase #2 $23.70   5.623%   $25.0327   $25.03   $25.05   $25.00  
  Purchase #3 $8.77   8.828%   $9.5442   $9.54   $9.55   $9.50  
  Purchase #4 $151.49   8.872%   $164.9302   $164.93   $164.95   $164.90  
  Purchase #5 $152.56   9.187%   $166.5757   $166.58   $166.60   $166.60  
  Purchase #6 $181.54   12.573%   $204.365   $204.37   $204.35   $204.40  
  Purchase #7 $233.36   12.621%   $262.8124   $262.81   $262.80   $262.80  
  7 purchase totals = $980.38       $1,081.5605   $1,081.56   $1,081.60   $1,081.50