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 $228.61   5.608%   $241.4304   $241.43   $241.45   $241.40  
  Purchase #2 $232.79   6.602%   $248.1588   $248.16   $248.15   $248.20  
  Purchase #3 $70.29   5.385%   $74.0751   $74.08   $74.10   $74.10  
  Purchase #4 $176.71   7.682%   $190.2849   $190.28   $190.30   $190.30  
  Purchase #5 $244.93   12.640%   $275.8892   $275.89   $275.90   $275.90  
  Purchase #6 $116.40   4.407%   $121.5297   $121.53   $121.55   $121.50  
  Purchase #7 $179.51   13.575%   $203.8785   $203.88   $203.90   $203.90  
  7 purchase totals = $1,249.24       $1,355.2466   $1,355.25   $1,355.35   $1,355.30