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 $53.81   6.278%   $57.1882   $57.19   $57.20   $57.20  
  Purchase #2 $184.39   8.826%   $200.6643   $200.66   $200.65   $200.70  
  Purchase #3 $32.39   4.718%   $33.9182   $33.92   $33.90   $33.90  
  Purchase #4 $218.71   3.857%   $227.1456   $227.15   $227.15   $227.10  
  Purchase #5 $181.66   5.723%   $192.0564   $192.06   $192.05   $192.10  
  Purchase #6 $166.54   4.720%   $174.4007   $174.40   $174.40   $174.40  
  Purchase #7 $164.61   4.206%   $171.5335   $171.53   $171.55   $171.50  
  7 purchase totals = $1,002.11       $1,056.9069   $1,056.91   $1,056.90   $1,056.90