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 $44.53   11.829%   $49.7975   $49.80   $49.80   $49.80  
  Purchase #2 $171.81   8.654%   $186.6784   $186.68   $186.70   $186.70  
  Purchase #3 $191.35   12.752%   $215.751   $215.75   $215.75   $215.80  
  Purchase #4 $147.91   9.376%   $161.778   $161.78   $161.80   $161.80  
  Purchase #5 $181.54   12.292%   $203.8549   $203.85   $203.85   $203.90  
  Purchase #6 $5.87   12.676%   $6.6141   $6.61   $6.60   $6.60  
  Purchase #7 $98.33   7.270%   $105.4786   $105.48   $105.50   $105.50  
  7 purchase totals = $841.34       $929.9525   $929.95   $930.00   $930.10