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 $128.50   4.732%   $134.5806   $134.58   $134.60   $134.60  
  Purchase #2 $216.87   4.637%   $226.9263   $226.93   $226.95   $226.90  
  Purchase #3 $20.48   11.134%   $22.7602   $22.76   $22.75   $22.80  
  Purchase #4 $207.96   12.250%   $233.4351   $233.44   $233.45   $233.40  
  Purchase #5 $123.35   8.794%   $134.1974   $134.20   $134.20   $134.20  
  Purchase #6 $186.98   11.456%   $208.4004   $208.40   $208.40   $208.40  
  Purchase #7 $128.48   11.569%   $143.3439   $143.34   $143.35   $143.30  
  7 purchase totals = $1,012.62       $1,103.6439   $1,103.65   $1,103.70   $1,103.60