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 $222.46   13.294%   $252.0338   $252.03   $252.05   $252.00  
  Purchase #2 $94.45   10.406%   $104.2785   $104.28   $104.30   $104.30  
  Purchase #3 $245.25   6.831%   $262.003   $262.00   $262.00   $262.00  
  Purchase #4 $37.45   7.642%   $40.3119   $40.31   $40.30   $40.30  
  Purchase #5 $196.35   8.109%   $212.272   $212.27   $212.25   $212.30  
  Purchase #6 $140.95   10.641%   $155.9485   $155.95   $155.95   $155.90  
  Purchase #7 $237.44   6.834%   $253.6666   $253.67   $253.65   $253.70  
  7 purchase totals = $1,174.35       $1,280.5143   $1,280.51   $1,280.50   $1,280.50