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 $110.74   11.449%   $123.4186   $123.42   $123.40   $123.40  
  Purchase #2 $101.64   12.404%   $114.2474   $114.25   $114.25   $114.20  
  Purchase #3 $162.49   8.374%   $176.0969   $176.10   $176.10   $176.10  
  Purchase #4 $54.89   8.709%   $59.6704   $59.67   $59.65   $59.70  
  Purchase #5 $65.36   5.631%   $69.0404   $69.04   $69.05   $69.00  
  Purchase #6 $133.35   10.818%   $147.7758   $147.78   $147.80   $147.80  
  Purchase #7 $121.25   10.270%   $133.7024   $133.70   $133.70   $133.70  
  7 purchase totals = $749.72       $823.9519   $823.96   $823.95   $823.90