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 $84.62   11.157%   $94.0611   $94.06   $94.05   $94.10  
  Purchase #2 $241.93   6.812%   $258.4103   $258.41   $258.40   $258.40  
  Purchase #3 $222.82   4.379%   $232.5773   $232.58   $232.60   $232.60  
  Purchase #4 $224.33   12.803%   $253.051   $253.05   $253.05   $253.10  
  Purchase #5 $118.51   4.237%   $123.5313   $123.53   $123.55   $123.50  
  Purchase #6 $237.75   13.278%   $269.3184   $269.32   $269.30   $269.30  
  Purchase #7 $18.36   12.710%   $20.6936   $20.69   $20.70   $20.70  
  7 purchase totals = $1,148.32       $1,251.6430   $1,251.64   $1,251.65   $1,251.70